Raising Spell DC

[pabelfly]

This thread was based off this original post by Morof Stonehands.

These threads are only as good as everyone else that assists in compiling them, so thank you for everyone for your help, no matter how minor.

Corrections and additions always welcome.

Quick Index
Ability Score Boosts
Races
Base Classes
Prestige Classes

Arcane
Divine

Feats
Domains
Spells
Items, Permanent Bonus

Alphabetical
By Price

Items, Consumables

Alphabetical
By Price

Other Spell DC Boosts

Ability Score Boosts
See here for a comprehensive guide to ways to boost ability scores, which also boosts spell DCs.

Races
Gnome (ECL 0) – +1 DC to illusion spells (Player’s Handbook)
Illumian (ECL 0) – The naenkrau sigil lets you leave up to two spell slots open to give +1 DC to all other spells of that level (Races of Destiny)
Spellscale (ECL 0) – Has the option of heightening spells 3/day (Races of the Dragon)

Jaebrin (1HD, 1LA) – +1 DC enchantment spells (Monster Manual V)
Svirfneblin (1HD, LA 3) – +1 DC illusion spells (Monster Manual)
Arkamoi (4HD, 4LA) – +1 DC to arcane spells for 1 minute after casting first arcane spell in encounter. Stacking +1, to max of +5 for each subsequent spell cast in that minute. All dissappear at end of minute. (Monster Manual V)
Hobgoblin Warsoul (10HD, 4LA) – Soul Tyrant to draw life out of hobgoblin ally, add +2 DC to next spell cast (Monster Manual V)
Zern (8HD, 7LA) +4 DC transmutation spells (Monster Manual IV)

Base Classes
Bard (Golarion Variant) – treated as being two levels higher for Bardic Music effects and save DCs (Pathfinder Campaign Setting)
Bard 6 (Spellscale) +2 save DC for Suggestion bardic music ability (Races of the Dragon)
Beguiler 2 , 14 – +1 DC to spells vs foes denied Dex to AC (Player’s Handbook II)
Hexblade 1 (School Mastery ACF, Transmutation) +1 DC whenever you cast a spell that alters a creature’s form, kind or type. (Dragon Magazine #357)
Hexblade 15 (Focus Caster, Enchantment ACF) – +2 DC to enchantment spells (Dragon Magazine #348)
Paladin of Tyranny 3 – Aura of Despair lowers saves by 2 (Unearthed Arcana)
Shugenja 1 – Gain Spell Focus, +1 DC for element type (Complete Divine)
Sorcerer 1 (School Mastery ACF, Transmutation) +1 DC whenever you cast a spell that alters a creature’s form, kind or type. (Dragon Magazine #357)
Sorcerer 5 (Dwarf Sorcerer ACF) – +1 DC to spell when both character and opponent are touching the ground (Races of Stone)
Sorcerer 15 (Focus Caster, Enchantment ACF) – +2 DC to enchantment spells (Dragon Magazine #348)
Wizard 1 (Arcane Duellist) – can increase a spell’s DC by 1, among other effects a number of times per day equal to INT bonus. (Pathfinder Campaign Setting)
Wizard 1 (High Diviner ACF) – give up familiar to gain +1 DC to divination spells (Unearthed Arcana)
Wizard 5, 15 (High Conjurer ACF) – +2/+4 DC to dispel conjured creatures (Unearthed Arcana)
[B][I]Wizard 10 (Illusionist ACF)[B][I] – give up bonus feat and gain +1 DC to illusion spells (Unearthed Arcana)
Wizard 10 (Planar Wizard ACF) – +1 DC to spells when cast against creatures of the opposed alignment of her chosen one. +2 DC if the spell normally has the chosen alignment (Planar Handbook)
Wizard 15 (Focus Caster, Enchantment ACF) – +2 DC to enchantment spells (Dragon Magazine #348)

Prestige Classes
Arcane Prestige Classes

Class	ECL for Bonus to DCs	Alignment	Spellcasting Progression	Bonus Description	Sourcebook
Divine Oracle 1	ECL 6		10/10	+1 DC scrying spells	Complete Divine
Dread Witch	ECL 4, 7		4/5	+1/+2 DC for Fear spells	Heroes of Horror
Dungeon Lord 5	ECL 10		0/5	+1 DC while in your dungeon against intruders	Complete Scoundrel
Elemental Savant 5, 10	ECL 10, 15		8/10	+1/+2 DC for chosen energy descriptor	Complete Arcane
Fatespinner 1	ECL 8		4/5	Add fatespin bonus of 1-5 to spell DC	Complete Arcane
Fatespinner 2	ECL 9		4/5	Make an enemy reroll, including a save reroll	Complete Arcane
Fatespinner 5	ECL 12		4/5	Make enemy to take -10 on next saving throw	Complete Arcane
Insidious Corruptor 6	ECL 13	Nonlawful	5/10	Release a subject to increase save DC of Charm spell by Cha modifier	Drow of the Underdark
Insidious Corruptor 7	ECL 14	Nonlawful	5/10	Makes subject cast spell at +2 DC at target you indicate	Drow of the Underdark
Insidious Corruptor 9	ECL 16	Nonlawful	5/10	Release a subject to increase save DC of Compulsion spell by Cha modifier	Drow of the Underdark
Keeper of the Cerulean Sign 2	ECL 7		10/10	+6 DC to spells that deal damage to aberrations, half class levels/day	Lords of Madness
Knight of the Chalice 4	ECL 12	LG	Independent, 4ths	+2 DC against evil outsiders	Complete Mage
Lifedrinker 3	ECL 6	Any Evil		Heighten Spell by using Lifepool points	Book of Vile Darkness
Magical Trickster 3	ECL 8		2/3	+1 DC on spell in same round you perform a skill trick	Complete Scoundrel
Master Specialist 4	ECL 7		10/10	+ 2 DC on " will disbelief" illusion spells	Complete Mage
Paragnostic Apostle 1-5	ECL 6-10		5/5	Backhanded Attack, spells with extra save against nondamaging effect, add 1 to DC	Complete Champion
Paragnostic Apostle 1-5	ECL 6-10		5/5	Discern Weakness Attack, +1 DC for spells against specific enemy type	Complete Champion
Paragnostic Apostle 1-5	ECL 6-10		5/5	Noble Prescence, +1 DC for spells that affect the subject’s emotions but don’t specify actions	Complete Champion
Paragnostic Apostle 1-5	ECL 6-10		5/5	See through the Veil, +1 DC for necromancy spells that target undead	Complete Champion
Rage Mage 5, 10		Nonlawful	5/10	Angry Spell +2/+4 DC when raging for abujuration, conjuration, evocation, necromancy, transmutation	Complete Warrior
Soulcaster 1, 7	ECL 6, 12		10/10, 10/10	Invest 1/2 essential in a spell to boost CL and DC by 1/2	Savage Species
Sybil 1	ECL 8		0/10	Add Sybil class level to WIS for spell DC for divine casters	Savage Species
Wild Soul 8	ECL 13	Nonlawful	9/10	+1 DC illusion spells	Complete Mage
Wild Soul 10	ECL 15	Nonlawful	9/10	+1 DC enchantment spells	Complete Mage

Divine Prestige Classes

Class	ECL for Bonus to DCs	Alignment	Spellcasting Progression	Bonus Description	Sourcebook
Divine Oracle 1	ECL 6		10/10	+1 DC scrying spells	Complete Divine
Divine Prankster 2	ECL 7		10/10	Spend Turn/rebuke attempt to add 10 to DC to disbelieve illusion spells	Races of Stone
Dread Witch	ECL 4, 7		4/5	+1/+2 DC for Fear spells	Heroes of Horror
Dungeon Lord 5	ECL 10		0/5	+1 DC while in your dungeon against intruders	Complete Scoundrel
Elemental Savant 5, 10	ECL 10, 15		8/10	+1/+2 DC for chosen energy descriptor	Complete Arcane
Fatespinner 1	ECL 8		4/5	Add fatespin bonus of 1-5 to spell DC	Complete Arcane
Fatespinner 2	ECL 9		4/5	Make an enemy reroll, including a save reroll	Complete Arcane
Fatespinner 5	ECL 12		4/5	Make enemy to take -10 on next saving throw	Complete Arcane
Insidious Corruptor 6	ECL 13	Nonlawful	5/10	Release a subject to increase save DC of Charm spell by Cha modifier	Drow of the Underdark
Insidious Corruptor 7	ECL 14	Nonlawful	5/10	Makes subject cast spell at +2 DC at target you indicate	Drow of the Underdark
Insidious Corruptor 9	ECL 16	Nonlawful	5/10	Release a subject to increase save DC of Compulsion spell by Cha modifier	Drow of the Underdark
Keeper of the Cerulean Sign 2	ECL 7		10/10	+6 DC to spells that deal damage to aberrations, half class levels/day	Lords of Madness
Knight of the Chalice 4	ECL 12	LG	Independent, 4ths	+2 DC against evil outsiders	Complete Mage
Magical Trickster 3	ECL 8		2/3	+1 DC on spell in same round you perform a skill trick	Complete Scoundrel
Paragnostic Apostle 1-5	ECL 6-10		5/5	Backhanded Attack, spells with extra save against nondamaging effect, add 1 to DC	Complete Champion
Paragnostic Apostle 1-5	ECL 6-10		5/5	Discern Weakness Attack, +1 DC for spells against specific enemy type	Complete Champion
Paragnostic Apostle 1-5	ECL 6-10		5/5	Noble Prescence, +1 DC for spells that affect the subject’s emotions but don’t specify actions	Complete Champion
Paragnostic Apostle 1-5	ECL 6-10		5/5	See through the Veil, +1 DC for necromancy spells that target undead	Complete Champion
Sybil 1	ECL 8		0/10	Add Sybil class level to WIS for spell DC for divine casters	Savage Species

Feats
See “Changing Spell Types” in this thread (Raising Caster Level) for information about ways to change or add new spell descriptors to take advantage of some options here.

Aberration Banemagic – +2 DC to spells that deal damage to aberrations (Lords of Madness)
Arcane Consumption – +4 bonus to spell DC on next spell you cast, become fatigued with -4 penalty to Con (Player’s Handbook II)
Battlecaster Offense – deal combat damage to foe for +1 DC to spells targeting that foe next round (Complete Mage)
Captivating Melody – sacrifice bardic music for +2 DC on enchantment and illusion spells (Complete Mage)
Cold Focus – +1 DC cold descriptor spells (Frostburn)
Cold Focus, Greater – +1 DC cold descriptor spells ( Frostburn)
Cooperative spell (metamagic) – add 2 to the DC when cast with another person, additional +1 for each extra person (Complete Arcane)
Demonic Conduct – feat, +1 DC against lawful or good targets, or +2 DC against lawful good targets (Fiendish Codex)
Draconic Power – +1 DC to spells of Draconic Heritage Energy Type (Acid, Cold, Charm, Electric, Fire, Force, Light, Poison or Disease, Sonic) (also increases caster level by 1)
Draconic Aura (Energy) – +1 to +4 to DC of spells of acid, cold, electricity or fire. Various ways to increase this bonus. See also Dragonblooded feat. (Dragon Magic)
Enchanting Song – spend bardic music use to add +1 to DC of enchantment spell (Races of Stone)
Enemy of Good – +2 DC to saves against good subtype creatures, or creatures with aura of good (Elder Evils)
Fey Power – +1 DC to enchantment spells (Complete Mage)
Fiendish Power – +1 DC evil descriptor spells (Complete Mage)
Heighten Spell (Metamagic) Increase spell level to increase spell DC (Player’s Handbook)
Hellsworn – +1 DC to evil descriptor spells 1/ encounter (Exemplars of Evil)
Heroes of Horror – Corrupt Spell Focus: feat, +1 DC for spells with corrupt component
Heroes of Horror – Greater Corrupt Spell Focus: feat, +1 DC for spells with corrupt component
Holy Potency – +Cha bonus to save against cure or inflict spell (Complete Champion)
Malign Spell Focus – +2 DC of evil descriptor spells (Book of Vile Darkness)
Metamagic Vigor – feat, cast two spells enchanced by metamagic in consecutive rounds, +1 DC for second spell (Complete Mage)
Misleading Song - spend bardic music use to add +1 to DC of illusion spell (Races of Stone)
Named Spell (Metamagic) +2 to save DC of spells with Truespeak check that target a single enemy (Dragon 346, p88)
Named Spell, Greater (Metamagic) +2 to save DC of spells with Truespeak check that target a single enemy, stacks with Named Spell (Dragon 346, p88)
Nocturnal Caster – +1 DC to specific school of magic when casting at night (Tome of Magic)
Pious Spellsurge – +1d6 DC with 2 faith points spent (Complete Divine)
Planar Touchstone feat (Stormvault site), +1 DC to spells involving rain, wind, lightning or clouds (Planar Handbook)
Sanctum Spell – raises spell level by 1 when cast in your sanctum (Complete Arcane)
Shadow Trickster – +2 DC illusion spells when in Shadow Hand stance (Tome of Battle)
Spell Focus (Good, Evil, Chaos, Law) – feat, +1 DC to alignment descriptor spells, does not stack with other spell focus feats (Complete Divine)
Spell Focus Good – (likely superseded by Complete Divine feat of same name) by +2 DC of good descriptor spells (Book of Exalted Deeds)
Spell Focus – +1 DC to chosen spell school (Player’s Handbook)
Spell Focus, Greater – +1 DC to chosen spell school (Player’s Handbook)
Spell Rehersal – cumulative +1 DC to spell cast in succesion 2 or more times
Tattoo Focus – +1 DC on specialized school spells (Dungeon Master’s Guide)
Vow of Non-violence – +4 DC for non-damaging spells (Book of Exalted Deeds)

Spells
Harmonic Chorus (Bard 3) – +2 morale bonus to spell DC (Spell Compendium)
Mystic Surge (Sorcerer 4, Wizard 4) – +2 DC to next spell cast by subject (Player's Handbook 2)
Spell Enhancer (Sorcerer 4, Wizard 4) – swift action, the next
spell you cast has +1 DC (and 2 CL) (Spell Compendium)

Items, Permanent
Alphabetical
Amulet of Fearsome Might 11K gold, +2 DC to fear spells, does not stack with Spell Focus (Dragon Magic)
Blood Face of Erythnul 100G, focus, +1 DC to illusion spells or spells with the Chaos descriptor (Complete Champion)
Greater Crystal of Arcane Steel 6K gold, Weapon Augment Crystal, +1 DC for touch channeled through weapon (Magic Item Compendium)
Icemail Armor 52K gold, +2 DC to Cold spells (Web)
Moradin's Forge 100G focus, +1 DC earth domain or earth descriptor spells (Complete Champion)
Regalia of Evil Unpriced, Artifact set, +2 DC to spells (Book of Vile Darkness)
Vecna's hand and eye 100G focus, +1 DC knowledge and magic domain spells (Complete Champion)
Veil of Allure: 14K gold, Item, +2 DC to enchantment spells (Magic Item Compendium )
Vest of Master Evoker 10K gold, +2 to spell DCs 3/day (Magic Item Compendium)
Wrymbane Helm Unpriced, Legacy Item, +2 DC to spells targeting dragons (Dragon Magic)

By Price
Blood Face of Erythnul 100G, focus, +1 DC to illusion spells or spells with the Chaos descriptor (Complete Champion)
Icemail Armor 52K gold, +2 DC to Cold spells (Web)
Moradin's Forge 100G focus, +1 DC earth domain or earth descriptor spells (Complete Champion)
Vecna's Hand and Eye 100G focus, +1 DC knowledge and magic domain spells (Complete Champion)
Greater Crystal of Arcane Steel 6K gold, Weapon Augment Crystal, +1 DC for touch channeled through weapon (Magic Item Compendium)
Vest of Master Evoker 10K gold, +2 to spell DCs 3/day (Magic Item Compendium)
Amulet of Fearsome Might 11K gold, +2 DC to fear spells, does not stack with Spell Focus (Dragon Magic)
Veil of Allure: 14K gold, Item, +2 DC to enchantment spells (Magic Item Compendium )

Regalia of Evil Unpriced, Artifact set, +2 DC to spells (Book of Vile Darkness)
Wrymbane Helm Unpriced, Legacy Item, +2 DC to spells targeting dragons (Dragon Magic)


Items, Consumables
Alphabetical
Angel Radiance 20G, +1 DC spell component, for spells of dismissal, banishment, dispel evil or to drive out evil fiends (Book of Exalted Deeds)
Angel's Blood 85GP, +1 DC component, evil desrciptor spells (Complete Champion)
Coutl Scale 16GP, possible +1 DC spell component, 30% chance of raising DC by 1 (Book of Exalted Deeds)
Crypt Powder 150GP, +1 DC component, spells targeting undead (Complete Champion)
Essence of Order 300GP component, +1 DC law descriptor spells (Complete Champion)
Lillend Scale 15GP, possible +L1 DC spell component, if spell requires a will save, 40% chance, 60% if caster is bard (Book of Exalted Deeds)
Metallic Dragon Heart 7GP, possible +1 DC component, 30% chance to increase DC by 1 (Book of Vile Darkness)
Soul in Larva Form 250GP, +2 DC component (Book of Vile Darkness)
Unicorn Blood 500G, possible +1 DC spell component, if spell requires a fort save, 40% chance to raise DC by 1 (Book of Exalted Deeds)

By Price
Metallic Dragon Heart 7GP, possible +1 DC component, 30% chance to increase DC by 1 (Book of Vile Darkness)
Lillend Scale 15GP, possible +L1 DC spell component, if spell requires a will save, 40% chance, 60% if caster is bard (Book of Exalted Deeds)
Coutl Scale 16GP, possible +1 DC spell component, 30% chance of raising DC by 1 (Book of Exalted Deeds)
Angel Radiance 20G, +1 DC spell component, for spells of dismissal, banishment, dispel evil or to drive out evil fiends (Book of Exalted Deeds)
Angel's Blood 85GP, +1 DC component, evil desrciptor spells (Complete Champion)
Crypt Powder 150GP, +1 DC component, spells targeting undead (Complete Champion)
Soul in Larva Form 250GP, +2 DC component (Book of Vile Darkness)
Essence of Order 300GP component, +1 DC law descriptor spells (Complete Champion)
Unicorn Blood 500G, possible +1 DC spell component, if spell requires a fort save, 40% chance to raise DC by 1 (Book of Exalted Deeds)

Other Spell DC Boosts
Energy (Draconic Aura) – +1 to +4 to DC of spells of acid, cold, electricity or fire. Various ways to increase this bonus. See also the Draconic Aura feat and Dragonblooded. (Dragon Magic)
Gnome Chanting Circle Rune circle, gives +1 DC to illusion spells cast by gnomes inside circle (Races of Stone)
Illusion Veil (brow soulmeld) – +1 DC to illusion spells (Magic of Incarnum)
Magestone (material) – +1 DC (Dungeonscape)
Monster of Legend (template) – +4 DC (Monster Manual II)
Necropolis of Dread (location) – +1 DC fear spells (Dungeon Master's Guide II)
Ocrus-Blooded template – +1 DC for Necromancy spells (Monster Manual V)
Sharulhensa, the Alabaster Towers (affiliation) – +1 DC to enchantment spells, (score 15-22) (Player’s Handbook II)
Temptation Domain – +1 DC to mind affecting spells against a chosen gender (Fiendish Codex)
Tyranny Domain – +1 DC compulsion descriptor spells (Complete Warrior)
Vale of Smoke and Fog (location), +1 DC illusion spells (Complete Mage)

[pabelfly]

Reserving this post.

Post away. Any suggestions are appreciated.

EDIT: Have to trawl through this to add anything I've missed in my initial search, will do this in a day or two
https://forums.giantitp.com/showthre...-Mini-Handbook

[Anthrowhale]

All the Circle Magic classes (Red Wizard, Halruaan Elder, Hathran) can circle magic heighten up to level 20.

The Circle Magic feat from Ghostwalk can heighten up to level 10.

I'm not sure how you want to handle indirect DC increasers, but:
a) Anything that increases your stats also increases spell save DC. This is particularly potent for Owl's Insight which can translate caster level into save DC at a 4-to-1 ratio.
b) There seems to be a dispute about whether DMM[Heighten] works, although in my understanding it should work.

[Saintheart]

Aa) Anything that increases your stats also increases spell save DC.

Maybe that's best handled by linking to a reasonably comprehensive ability score handbook, like this one.


Also, if Fatespinner 2-5 is going to be in there, that seems to invite whether indirect methods of raising spell DC (i.e. by nerfing saving throws) need to be mentioned. That's a very big subject on its own. Still, if Fatespinner 5 is up for consideration because it smashes saves by -10, then Doomspeak (Champions of Ruin) is probably worth noting too since it does the same thing for 1 round anyway.


Also also, there's the nonstandard spell DCs thing, where the operative DC works on a different formula to that of the standard 10+spell level+casting stat. e.g. Poison calculates its DC as 10+0.5*caster level+Wis mod. DC-raising effects will work for these, obviously, but there's at least a different mechanism to access, i.e. boosting caster level, which I seem to remember you had some notes on :).

A quick and dirty list of the spells I've seen that have this mechanic:

Kiss of Death (MoTW, Drd 5): As Poison (below), but druid-only and a fifth level spell.
Mind Poison (SpC, Sor/Wiz 3): Fort save is DC 10+0.5*caster level+Int/Cha for Sor/Wiz respectively
Poison (SRD, Clr 4, Drd 3): Fort save is DC 10+0.5*caster level+Wis
Poison Thorns (SpC, Drd 5): Fort save is DC 10+0.5*caster level+Wis. Druid-exclusive spell.
Spider Poison (SpC, Ass 3, Sor/Wiz 3): Fort save is DC 10+0.5*caster level+caster’s Int/Cha for wizards/sorcerers respectively (no love for the Assassin who can also cast the damn spell ☹ )

[pabelfly]

Maybe that's best handled by linking to a reasonably comprehensive ability score handbook, like this one.


Also, if Fatespinner 2-5 is going to be in there, that seems to invite whether indirect methods of raising spell DC (i.e. by nerfing saving throws) need to be mentioned. That's a very big subject on its own. Still, if Fatespinner 5 is up for consideration because it smashes saves by -10, then Doomspeak (Champions of Ruin) is probably worth noting too since it does the same thing for 1 round anyway.


Also also, there's the nonstandard spell DCs thing, where the operative DC works on a different formula to that of the standard 10+spell level+casting stat. e.g. Poison calculates its DC as 10+0.5*caster level+Wis mod. DC-raising effects will work for these, obviously, but there's at least a different mechanism to access, i.e. boosting caster level, which I seem to remember you had some notes on :).

A quick and dirty list of the spells I've seen that have this mechanic:

Kiss of Death (MoTW, Drd 5): As Poison (below), but druid-only and a fifth level spell.
Mind Poison (SpC, Sor/Wiz 3): Fort save is DC 10+0.5*caster level+Int/Cha for Sor/Wiz respectively
Poison (SRD, Clr 4, Drd 3): Fort save is DC 10+0.5*caster level+Wis
Poison Thorns (SpC, Drd 5): Fort save is DC 10+0.5*caster level+Wis. Druid-exclusive spell.
Spider Poison (SpC, Ass 3, Sor/Wiz 3): Fort save is DC 10+0.5*caster level+caster’s Int/Cha for wizards/sorcerers respectively (no love for the Assassin who can also cast the damn spell ☹ )

Ability score link added in. Good suggestion, thank you.

So for lowering save DCs, I'll only include ways that do it without requiring a saving throw (or similar). For the intent of wanting to be a more effective spellcaster, boosting your spell DC is nearly the same as lowering the opponent's saving throw with no save allowed, but if the effect can miss that's not nearly as consistent (or something I'm interested in cataloging). It is a bit arbitrary, but sometimes you have to put limits on what you'll include in these miniature handbooks, otherwise I'll never have the motivation to finish it.

Oh, and I'll include the list of spells with a nonstandard DC score like you give. It's definitely interesting enough to include if you're intent on boosting save DCs.

[Saintheart]

Ability score link added in. Good suggestion, thank you.

So for lowering save DCs, I'll only include ways that do it without requiring a saving throw (or similar). For the intent of wanting to be a more effective spellcaster, boosting your spell DC is nearly the same as lowering the opponent's saving throw with no save allowed, but if the effect can miss that's not nearly as consistent (or something I'm interested in cataloging). It is a bit arbitrary, but sometimes you have to put limits on what you'll include in these miniature handbooks, otherwise I'll never have the motivation to finish it.

Noted and I get the desire to not blow out scope more than is needed.

In that vein, then, one rough category is bestowing negative levels, since amongst other effects, negative levels nerf a target's saving throws by 1. That said not many methods of bestowing negative levels come as no-save or no-roll options. (Enervation I think is the best all-round method for doing this since it can do 1d4 negative levels at a time, doesn't allow a saving throw to the negative levels, but of course it takes a ranged touch attack to hit.)

If one were looking for no-save methods of bestowing negative levels, there's two pretty situational methods I can think of:
(1) Cast Planar Bubble on a Xeg-Yi, which is an outsider native to the Negative Energy Plane. The area for 20 feet around it then behaves like the Negative Energy Plane, i.e. bestow negative levels once per round (no save) on anything standing in it.
(2) Be a Planar Shepherd 5, do exactly the same thing, only on yourself.

[Anthrowhale]

In terms of save penalties, Unseelie Fey's "Winter Chill" option imposes the Fey's Cha bonus as a morale penalty to all saves of non-fey within 5'. The range is limiting but could be effective on a sorcadin build.

[Saintheart]

In terms of save penalties, Unseelie Fey's "Winter Chill" option imposes the Fey's Cha bonus as a morale penalty to all saves of non-fey within 5'. The range is limiting but could be effective on a sorcadin build.

In a similar vein: the Paladin of Tyranny (SRD) has an Aura of Despair that does an untyped no-roll -2 to saving throws within 10'.

I could've sworn the Hexblade's hex was the same, but it unfortunately does come with a Will save.

[ExLibrisMortis]

Edit: Of course I meant to lead with "This is a very good list, thanks!". So, uh, that.

The Mind Mage (Dragon 313) has some DC-increasing abilities.
At level 3, you get +1 to spell save DCs as long as you have at least 5 pp remaining.
At level 9, you get +2 to spell save DCs as long as you have at least 10 pp remaining. Overlaps with the third-level ability.
At level 10, you can add your casting and manifesting ability modifier together when casting psi-spells (that is, spells cast and powers manifested with a psi-spell feat applied). That can increase the DC quite a bit, especially if you have the same casting and manifesting stat (which is pretty common).

You also get the ability to Heighten a psionic power by one, class level times per day. 3.0 still had Heighten Power, and the mind mage was written with the EPH in mind but without a clear picture of what all was going to get changed. It turned out pretty great, but it has some 3.0isms in there.

[Anthrowhale]

Earth Spell adds +1 DC to spells that are heightened when standing on the earth.

[Troacctid]

I could've sworn the Hexblade's hex was the same, but it unfortunately does come with a Will save.

You're probably thinking of the dark companion variant from PH2.

[Inevitability]

Prophet of the Divine, Power of Faerun. +4 to the DC of compulsion spells (and SLAs and SUs) if you cast them within 3 rounds of a spell that lets you communicate with your deity (like Augury, or, more cheaply and practically, Omen of Peril). Not too practical in combat, but great when casting something like Zone of Truth in a social situation or trying to Dominate a helpless prisoner.

[ShurikVch]

Base Classes
Druid, Wind Walker 1 (Dragon #311): Zephyr Spellcasting - +1 DC and CL for [air] spells
Druid, Winter Warden 1 (Dragon #311): Cold Casting - +1 DC and CL for [cold] spells
Wizard, Fleshcrafter 15 (Dragon #312): Master of Life and Death - +1 DC vs living creatures

Prestige Classes
Cataclysm Mage 7 (Explorer's Handbook): Ashtakalan Secret - +1 DC to spells of Enchantment (charm) subschool
Dancer of Sharess 7 (Dragon #290): Wiles of the Pleasure Queen - +2 DC to spells of Enchantment school
Dragon Mystic ? (Dragon #296): Draconic Spell Focus - +2 DC to spells which do the same type of energy damage as your Breath Weapon
Eunuch Warlock 1 (Oriental Adventures): Greater Spell Focus - +4 DC for spells of all schools for which you have Spell Focus (including those for which you would take Spell Focus later)
Thrall of Dagon 4 (Dragon #349): Voice of Rapture - +1 DC for language-dependent spells
Thrall of Fraz-Urb'luu 1+ (Dragon #333): Deception - +1 DC for spell of Illusion school; limited times/day - from 1/day at 1st level to 5/day at 9th
Thrall of Malcanthet 4 & 8 (Dragon #353): Charming Voice - +1 DC for language-dependent spells; Dominating Voice - +2 DC for language-dependent spells

Feats
Blood Sorcerer (Oriental Adventures) - +3 DC to all Maho-Tsukai spells
Bloodline of Fire (Player's Guide to Faerûn) - +2 DC on [fire] spells
Charmer (Dragon #325) - +1 DC to spells of Enchantment (charm) subschool (stacks with Spell Focus)
Commanding (Dragon Compendium) - +1 DC to spells of Enchantment (compulsion) subschool (stacks with Spell Focus and Greater Spell Focus)
Corrupt Arcane Studies (Ghostwalk) - +1 DC to all Sorcerer and Wizard spells
Elemental Focus (Dragon #319) - +1 DC to all [air], [earth], [fire], or [water] spells (stacks with Spell Focus and Greater Spell Focus)
Genie Lore (Races of Faerûn) - chose one energy descriptor, get +1 DC for Sorcerer spells with this descriptor (stacks with Spell Focus)
Heir of Lendore (Dragon #319) - +2 DC for spells of Divination school
Jinnbond (Dragon #319) - +2 DC on spell with a selected descriptor (Dao - [earth], Djinni - [air], Efreeti - [fire], Marid - [water])
Lore of the Ur‐Flan (Dragon #315) - +2 DC for all [Evil] Necromancy spells
Reverberation (Savage Species) - +2 DC on [sonic] Special Attack; since spells are Special Attacks...
Sacred Tattoo (Races of Faerûn) - +1 DC for spells you cast in an area Consecrated/Desecrated or Hallowed/Unhallowed to your deity
Shadow Weave Magic (Player's Guide to Faerûn) - +1 DC on spells of Enchantment, Illusion, or Necromancy school
Spellcaster Support (Oriental Adventures) - +2 DC on spells of allied Shugenja

Items, Permanent
Archmage's Hat (Dragon #314) - by casting a spell as a Full-Round Action, add 150% or 200% of your Int mod to the spell's DC (doesn't works for non-Int-based spellcasting); Unpriced
Dagger of the Fireheart (Dragon #350) - +4 DC on (charm), [fire], and Necromancy spells; [Relic]; Unpriced
Gems (Magic of Faerûn) - +1 or +2 DC for a spell from a Wand (depending on the gem and spell); 1,000 or 5,000 gp
Might Stone (Dragon #356) - invest your Spell Known into the Stone (temporary "losing" it), get +2 DC for spells of the same school for times/day equal to the invested spell's level; 28,800 gp
Rings of the Spider (Dragon #318) - Drow with this ring get +1 DC for their Enchantment, Evocation, or Necromancy spells; 6,000 gp
Robe of Transmutation (Dungeon #124) - +1 DC for all spells which change the target's shape; 140,000 gp
Tasha's Grinning Idol (Dragon #359) - +2 DC to spells of Enchantment school; 28,000 gp

Items, Consumables
Oil of the Lamia (Book of Vile Darkness) - when applied to a magic item which produces an effect requiring a foe to make a saving throw, +2 DC vs Good creatures for 1 hour; 2,000 gp
Panaeolo (Lords of Darkness) - +2 DC of arcane spells for 1d4 hours; 250 gp

Other Spell DC Boosts
Saint template (Book of Exalted Deeds): Holy Power - +2 DC for all spells, SLA, Su, and Ex Special Abilities

[Saintheart]

Runecaster 10 (Players Guide to Faerun): +3 to DC of any spell you cast, added by tracing a rune in the air, becomes a somatic component of the spell. However, increases the casting time of the spell to a minimum full round action.


EDIT: Also...

Reverberation (Savage Species) - +2 DC on [sonic] Special Attack; since spells are Special Attacks...

By this reasoning, Ability Focus (feat) (Savage Species) also gives you +2 DC to all spells, since spells are Special Attacks :)


EDIT: Also also...

Giant Banemagic (Secrets of Xen'Drik) - as Aberration Banemagic from Lords of Madness, but against giants. +2 to DC.



EDIT: Also also also on no-roll nerfs to saving throws:

Battle Magic Tactics (Monster Manual 5, p. 84): Summing up, for every spell with a saving throw that you cast on a target, that target takes a -1 to their saves against your spells (or anyone else who's got this feat) until the end of the round. Best use if you can gatling-gun a lot of spells, or you've got a bunch of spellcasting friends together.

[Daisy]

Do any of these methods raise the DC of an SLA, e.g. a Warlock's invocations? I realise that anything affecting a specific school is unlikely to, but what about the others?

[Saintheart]

Do any of these methods raise the DC of an SLA, e.g. a Warlock's invocations? I realise that anything affecting a specific school is unlikely to, but what about the others?

There's Heighten SLA in C.Arcane if it helps...

[Daisy]

There's Heighten SLA in C.Arcane if it helps...

Yeah, I considered that. Quite "expensive" for what it does. I was hoping for something a bit more universal, like the Veil of Allure. But Warlocks just don't get the love that Wizards do.

[ShurikVch]

By this reasoning, Ability Focus (feat) (Savage Species) also gives you +2 DC to all spells, since spells are Special Attacks

The important detail there is "Special Attacks": every spell is a separate Special Attack (and thus - legal for Ability Focus feat)

[pabelfly]

Do any of these methods raise the DC of an SLA, e.g. a Warlock's invocations? I realise that anything affecting a specific school is unlikely to, but what about the others?

I'd have to comb through each ability to check the wording. Maybe I'll do a separate section on it, seems like it would be worth doing.

Specifically for SLAs, Boost Spell-Like Ability gives you +2 to three of your spell-like abilities three times a day. You can pick three of the same ability for that day, or three different abilities for that day, and you can take the feat repeatedly

As for the other suggestions, will try to add them to the thread tomorrow. Had work to catch up on and wanted to catch up on the reading for PHB II. Thanks for your patience.

[Saintheart]

One more, this one on nerfing saving throws with no-roll options: a Teamwork Benefit.

Spell Barrage (Dungeon Master's Guide 2, p. 193): Leader needs Spellcraft 8 ranks, team members 2 ranks. When a team member casts a spell needing a Reflex save, all enemies take a -2 on subsequent Reflex saves for each subsequent Reflex save made during that round due to other team members. Functions whether or not an opponent makes a save. The benefit itself suggests cheesing this by having UMD rogues cast reflex-drawing spells from wands in order to nerf targets’ saves before the mage comes in with his big blasty spell.

EDIT: Also, while trawling around in Caedrus' Fear Handbook for nerfs to saves, I found a couple of surprises:

Unnatural Aura (Dragon Magazine, Issue 356, Page 89). Taken at 1st level, this trait costs you a -2 penalty for all interactions with animals and vermin. The (untyped) bonus is a +2 on all Intimidate checks and to +2 DC of all spells with the [Fear] Descriptor.

Amulet of Fearsome Might (Dragon Magazine, Issue 332, Page 70). Doubles the radius of the wearer’s innate frightful presence, and increases the DC to save against it by +2. In addition, any spells (or spell-like abilities) with the [Fear] descriptor cast by the wearer have their DC increased by +2. It doesn’t stack (explicitly) with the feats Spell Focus or Greater Spell Focus. This item has a CL of 7, costs 11,100 g.p, weighs 1 lb. and takes up the throat slot.