Heath Ledger (The Joker in Chris Nolan's Dark Knight) told the Toronto Sun: "It's definitely going to stump people. I think it'll be more along the lines of how the Joker was meant to be in the comics, darker and more sinister."
The Toronto Star also got Ledger to admit his casting in the Batman Begins sequel was a surprise, even to himself. "I wouldn't have thought of me, either. But it's obviously not going to be what Jack Nicholson did. It's going to be more nuanced and dark and more along the lines of a Clockwork Orange kind of feel. Which is, I think, what the comic book was after: less about his laugh and more about his eyes."
Meanwhile, Bob Hoskins (Hollywoodland) has been rumored for the role of the Penguin. But the actor told IESB that he's not been offered the role but would like to take it on. See a short video interview here (Windows Media Player required).
Filming begins in January for a June 2008 release.