As the others said, some quick notes and ideas (and nitpicks)

Barbarian: Danger sense adding more bonuses to AC in combat? This sounds a lot like the monk's bonuses to AC(even though he doesn't lose then when flatfooted). Adding it to all Reflex bonuses is cool, though.

Monk: The 1:1 Power Attack ratio already exists. The Power Attack feat entry especifies that unarmed strikes are always 1:1, even if US are usually treated as light weapons. Just to let you know. Giving him the ability to flurry as a default action gives him a much needed boost.

Sorcerer: I think the game already allows you to replace spells every 4 levels. Allowing it every level looks fine.

Fighter: You want to give him bonus feats to fill in the dead levels. As someone pointed out, it looks weird. Here's the mini-fix I did a long time ago, you may like it as it's simple, and makes it look like class features:
Spoiler
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1st level: Weapon Improvisation: You can use improvised weapons, and unproficient exotic weapons at -2, instead of -4. You are still not proficient with these weapons, unless you gain the related feats, as normal.
3rd level: Weapon Focus: You gain a generic +1 bonus to attack rolls when attacking with any weapon.
5th level: Weapon Specialization: You gain a generic +2 bonus to damage rolls when attacking with any weapon.
7th level: Armor Focus: The armor check penalty of any armor is reduced a given number (minimum 0) when you wear it. The reduction is 1 point for light armor, 2 for medium armor, and 3 for heavy armor.
9th level: Armor Specialization: The base armor bonus from any armor is increased a given number when you wear it. The bonus is +3 for llight armor, +2 for medium armor, and +1 for heavy armor.
11th level: Double strike: You can make two attacks as a default action. The first attack is made at your highest BaB bonus, the second at your highest BaB bonus with a -5 penalty.
13th level: Weapon Mastery: Choose a type of weapon: Melee slashing, melee puncturing, melee bludgeoning, ranged. You gain a +1 bonus to attack rolls and +2 bonus to damage rolls with weapons of that type. It stacks with the bonuses from Weapon Focus and Weapon Specialization
15th level: Double Step: You can make 10ft adjust moves, instead of 5ft adjust moves.
17th level: Armor Mastery: The size category of any armor you wear is reduced in one size category (minimum light). While wearing light armor you gain, instead, an additional +1 bonus to it's base AC. Doesn't stacks with Mithral armor.
19th level: Weapon Supremacy: Choose one weapon of the same type you choose for Weapon Mastery. You gain all the benefits of the feat Weapon Supremacy for that weapon (Player's Handbook 2). For ranged weapons, instead of being able to use it in grapple, you can attack without provoking attacks of opportunity.
20th: Armor supremacy: Your armor's armor bonus is changed into a deflection bonus, and also added to your Reflex saves.

Notes: All bonus from Weapon focus, specialization, mastery, and supremacy only applies to weapons you are proficient with.
All bonus from Armor focus, specialization, and supremacy applies only to armors you are proficient with, and doesn't apply to shield.
You can remove these feats (weapon focus, specialization, mastery, supremacy) from the feats list, as only the fighter uses them anyway.
This change gives a figther the whole Weapon Focus feat chain (that is considered weak), leaving him free to use his feats to something else, and encouraging a player to go all 20 levels to get some interesting bonuses, and giving him something every level. It may look overpowered at first, but in the end, it just gives the fighter a little boost, and gives him unique things.