KaeYoss said:
You can also use your AoO against spellcasting to "disarm" them, taking away their components or holy symbols. Or you make a trip attack, for if you are face-down in the dust, you'll have hard time finishing your incantations!
I don't think you can actually use an AoO to disarm them, although I may be wrong on this: I think you have to use the "attack an attended object" rules. The reason I rule this way is:
1) Those rules are there, so you may as well use them; and
2) Whereas you have to stick a weapon into someone's personal space in order to wound them, you can keep spell components and holy symbols close to your body, making it harder for someone to knock them out of your hand.
As for the trip attack, I've been wondering this same thing. What sort of Concentration check would be required to finish a spell while being tripped? Keep in mind that you can continue casting a spell even if someone smacks you on the head with a greatclub while you're casting it, as long as you make your Con check.
I'm thinking this would require a DC 15 + spell level Concentration check to avoid losing the spell. It's still a pretty good tactic for a fighter.
Of course, a better tactic is to grapple the wizard: unless the wizard is holding a dagger in her off-hand, your grapple is very likely to succeed (no AoO if your target is unarmed), and if your grapple succeeds, the spell automatically fails unless it has no somatic component.
Daniel