I second that. Laughing while you think you're falling to your death is pretty sweet.
For me it's a tie between the fake Batman hostage laugh and the Interrogation Room laugh.
Almost twenty years of Mark Hamill as the Joker will do that.
I'm gonna have to go with the interrogation room laugh if I had to pick just one. He's in total bliss as Batman lays into, beating him to a bloody pulp in rage because it's all he can do. To quote my mother, "he's sick" and he really is and this laugh, the laugh of a demented man taking glee in the pain of others, that's the Joker right there.
Honestly, my favorite wasn't even in the movie. It was the alternate take during the batpod/semi chase that was in the first trailer.
Heres a neat combo of his laughs http://www.youtube.com/watch?v=SgWf_vETKMQ
Gotta' be the self-mocking laugh when he crashes the mob meeting.