My favorite monks:
From Oriental Adventures:
Shintao Monk - I think they're supposed to be Rokugan's version of Shaolin monks. They've got some nice abilities, but most importantly, they gain a bonus martial arts feat every other level! Those bonus feats really help when it comes to mastering martial arts styles (as described in OA).
Tattooed Monk - A monk that gets magic tattoos every other level. Some of them are pretty killer, like damage resistance and haste self.
From Dragon magazine:
Acolyte of the Fist - Channel supernatural powers through your fist. Heal instead of harm with your punches. Choose your damage type, slashing or piercing damage instead of bludgeoning (piercing damage? what kind of unarmed attack is that, the eye gouger?). Channel force blasts through your fist, or shroud it in energy (fire, lightning, cold, acid, sonic).
From Path of the Sword:
Ki Warrior - Use ki power to perform supernatural feats, like smashing inanimate objects, attacking everyone within melee range, and throwing energy balls (fire or electricity).