Sudden Strike! (3.5 DnD)

[Zaydos]

If the fighter can find a way to fly the ninja/rogue can find a way to true see.

I'd point out that fly is a 3rd level spell, not too hard to get. True seeing is a 6th level spell (5th for cleric) with expensive material component (250 GP) that means your wizard buddy probably won't be willing to cast it on you and magic items that grant it will be prohibitively expensive.

[Cieyrin]

Whats the ambush feat?

Persistant Attacker.

[Darrin]

What are reliable ways of denying your opponent his dexterity bonus?

Someone has already mentioned marbles (A&EG p. 24). They work like caltrops, so they take a standard action to deploy. You can improve this by buying/training an animal with hands (monkey, ape, dire ape, etc.) to do this for you, which brings this down to a move action (handle animal check). You can improve it to a free action by getting a familiar/animal companion/wild cohort to do it for you.

Grappling is another good way to deny someone their Dex bonus, and if you can't get get someone else in the party to grapple for you, you can train animals to grapple with the Pin trick or the Hold trick (Masters of the Wild p. 19). Something with Improved Grab such as a crocodile or one of the bears makes a good start, although you can buy a bunch of mules (large animal, +9 grapple check) for really cheap (8 GP each). Warbeasts (MM2 template) aren't that expensive, about 50-75 GP per HD, so a trained polar bear warbeast only costs 775 GP, and a trained dire bear warbeast (grapple check +23!) only costs 1075 GP.

You can be your own grappler by picking up Improved Grab yourself, either via Spirit Bear Totem Barbarian (CompChamp), Wildshape and/or Bear Warrior, Scaled Horror (Savage Species, use the Aquatic template in Stormwrack to qualify), or Scorpion's Grasp feat (Sandstorm). This gives you the option to consider yourself outside the grapple, allowing you to finish your full attack on a grappled target. Add a Blurstrike weapon, and so long as your first attack hits, all your attacks will get Sudden Strike damage.

Grease is always a favorite, but there are cleric and druid versions of it, and all three are available with one-level dips or UMD (use the Skill Knowledge feat in Unearthed Arcana/SRD to pick it up as a class skill if need be). If you don't want to ding up your BAB, Duskblade + Arcane Disciple + one of the Slime deities can add Grease to your known spells. Ghaunadaur (drow deity) has slime, and if you dig into some of the more obscure corners of the FR books, Moander (dead god of rotting) and Ilsensine (illithids) give access to the slime domain. For clerics, there's the Ice Slick spell (Frostburn, 20' square), and for tree-huggers, there's Path of Frost (Dragon Magic, a little harder to use).

Invisibility is good, but it can be difficult to keep up, and at higher levels there are too many counters (see invis, true seeing, blindsight/sense, tremorsense, lifesense, etc.). Ring of Blinking + Pierce Magical Concealment feats can be extremely effective.

Outside of Ghost Step, the best way for a ninja to get sudden strike working is Blindness. There are a variety of alchemical/magic items that can blind, such as: Flash Pellets (Complete Arcane), Flashstone (Dragon Compendium, a little better than the CompArc version), Everbright weapons (MIC), Powder of the Black Veil (MIC). The absolute best blinding item is in Oriental Adventures. Eggshell grenade, dust version. A direct hit blinds the target for 1d4 rounds *no save*, and anyone else within 5' gets a Fort save.

If you're willing to dip a little deeper into a casting class, there are some great blinding spells. Glitterdust is always a favorite, but in the Spell Compendium take a look at Blinding Spittle (Druid 2). Ranged touch attack, -4 penalty, another *no save*. There's also the various fog/cloud spells, illusionary walls, and so forth. You can add the eggshell grenade to your full attack with the Rapid Shot feat.