Two AoO tricks
1) Grand Master of Flowers: There is an item in 3e's Arms & Equipment that teaches Monks to take 10ft steps instead of 5ft steps. Using that and a small selection of feats (combat reflexes, evasive reflexes, & robilar's gambit) I've created a Grandmaster who is nigh untouchable in melee combat (you roll to hit in melee, he gets a 10ft step...)... weakness: monsters with reach!
edit: perhaps worth noting that on his turn, the Grand Master of Flowers also has a 25ft reach with his UA attacks.
2) Iaijutsu is Broken: OA's Iai-Master has only gotten more powerful as new books have been released.
*Mercurial Strike (Dragon Compendium): if you're allowed an AoO while unarmed, you get to draw your blade and strike... and foe is FLATFOOTED
*Robilar's Gambit (PHBII): If opponent attacks you, gain an AoO (while taking some penalties).
Clearly these two feats tie in very nicely with the Iaijutsu Focus skill and are horribly borken with the Iaijutsu Master.
edit: I've used the above together along with another Dragon-mag feat that gives you iteritive AoO attacks... you attack me, I Iai-strike you, and then dance back 10ft before your corpse hits the floor (or, more rarely, you get to attack back).
Ahh, goodtimes.