This thread has some really inspired casting, and some that just don't sit well with me. The thing is, there's already been an amazing cast assembled, and they're all talented actors, with maybe the exception of Holmes, though she did just fine.
What they have done is proven that multiple villains can work together, but not in the overly-campy "Hey, we all hate Batman, so let's fight him together! Huzzah!" kind of way that Schumacher loved so very, very much.
There's no doubt in my mind that Martin Short is the Mad Hatter, but I really don't want to see him. Although I have no doubt Nolan and Goyer could pull it off, I can't see him translating as any more than a pseudo-replacement for the Scarecrow.
Christopher Lloyd would fit well with the cast already in place, and he really needs to pull himself out of the chasm that he's dug for himself lately (read: Stacked). He would be a terrific choice for the icy persona of Fries, but there's something really itching me to see him as the meticulously timed Clock King, including that Clockstoppers-like device he had in his second TAS appearance. It's just far-fetched enough to provide an interesting hyper-reality to the films.
I could see the Ventriloquist and Scarface as one of many people to fill in the vaccuum that Falcone was sure to have left. Rick Moranis, for anyone who's seen Little Shop of Horrors, is as great a casting as I could hope to see. Not sure who would be Scarface, though I like the idea of Kevin Pollack. The Ventriloquist would be another person that would fit well into the "altered perception of the world" category, like Scarecrow. I can see them doing a very Calvin and Hobbes-like trick with this. Everyone else sees Moranis holding a puppet. Moranis sees a living, breathing entity parading around him, and talking only through him. It would make for a great cinematic end to have Scarface be destroyed, leaving Moranis alone for the first time. It could actually make you feel bad for the Ventriloquist at the same time you felt justice was served with the destruction of Scarface.
I would rather not see Penguin as the drooling monster he was in Burton's movie, not that DeVito wasn't great, and that it wasn't an amazing movie, but we've seen that before. My choice would definitely be Bob Hoskins. After seeing Unleashed, it's hard to see him as Mario anymore, and anyone who's seen that Don Quixote movie they made a while back knows he's got the acting chops to pull it off.
As for Hugo Weaving and/or Willem Dafoe. I'd really like to see either of them in this, though I'm leaning more towards Hugo. He's just a great dramatic actor. I could see him as either the Riddler, or Fries. Either choice would make me ecstatic.
Joker, I could see Jason Lee doing him, I could see Crispin Glover doing him, I could even see Hamill doing him, but there's no point in fighting over who he's going to be. Nolan and Goyer have not let me down so far, and I doubt they'd set all this up so meticulously only to be a big letdown. We're going to get a top-notch. Joker-worthy performance no matter who they choose.