It kicked all kinds of ass. And Heath Ledger's Joker is easily the best comic book villain to appear in a movie. Aaron Eckhart's Harvey Dent/Two Face wasn't too shabby either. But since The Dark Knight has already made enough money to build a solid gold Batmobile, there will absolutely be a third movie in the series. Which means Christian Bale's Batman will need someone to administer beatings to.
I'll check in from time to time to discuss a candidate in detail until they announce the choice(s) or I run out of Batman villains, whichever comes first. Pros, cons, my random guess at who could play the character, and how I'd go about adapting the character for the big screen. And please offer your thoughts in the comments!