I like the suggestion of Willem Dafoe.
Vincent Cassel looks the part and can be crazy but I'm skeptical of his heavy French accent.
Same with Javier Bardem's thick Spanish accent.
Adrien Brody looks the part, but I'm not sure if he could act it.
I liked the idea of Paul Bettany back when TDK casting rumors were flying around, and I still think he could be good. He looks the part, and Gangster No. 1 showed he can be crazy enough. In fact, he's halfway to being The Joker in that movie.