Actually, Heath Ledger is the Joker. If you look around, you can find a picture of him in his makeup- and he looks like he describes it- a really scary clown.
I'm actually excited for a few reasons-First, they MIGHT show the Joker's true origins, which would be awesome. Second, they're dealing with something that I think I've only ever seen in Frank Miller's books- how Batman feels about copycat vigilanteism. And Third, we get to see Harvey Dent as a good guy- something that hasn't been covered since Billy Dee Williams held the role in good ol 1990.
I'm really excited about this movie.
-kv