Back onto the subject of TDK/possible villains in the sequels... I suspect (okay, I hope) Dent is still alive; the coin landed with the unscarred head up before the fall, and there was the whole "broken legs" scene with Maroni earlier that made me doubt that he's really dead. There's been a lot of talk of Catwoman. The two best actresses I can think of for Catwoman are actually Rosario Dawson and Eva Mendes, both largely for the same reasons -- they can be seductive, a little crazy, and a bit bad. See Gail in "Sin City" and... er. Whatever the detective dame's name was in "Once Upon A Time in Mexico" to see what I mean. There's also been talk of The Riddler. Fuck. That.
Another distinct possibility (one I'd be quite disappointed in) is casting an "older" Joker and basically recreating DKR. But that'd mean Robin. Robin bad. Plus, I really don't think anyone can hold a candle to Ledger's performance.

"Ah good. Now I'm on the internet clearly saying I like tranny cleavage. This shouldn't get me harassed at all."
-- Lothar of the Hill People