I plan on writing a much lengthier post about The Dark Knight, and especially about Heath Ledger's portrayal of the Joker. But I want to get this bit out first.
It took me a while to figure out what it is about the Joker in this movie that strikes me as so fascinating and familiar and yet so terrifying, but I think I have it: Ledger takes the intense psychosis of Hannibal Lecter and mixes in the coyote characteristics of Daffy Duck. There's likely a lot more to it than that, but I've seen the movie three times now -- you tell me:
(The Joker was always my favorite villain, and Daffy is one of my favorite Warner Brothers characters, so maybe I'm predisposed to pick out similar behaviors.)