I have a hard time thinking about it. I'm tempted to say Mickey Rourke oughta play Batman, but that doesn't seem proper somehow.
Here's what I'm thinking at the moment;
Batman - Robert DeNiro, if he can get into shape Raging Bull style.
Robin - Hillary Swank
The Joker - David Bowie
Harvey Dent - Edward James Olmos
Superman - Arnold Schwarzenegger (think about it--it makes too much sense)
James Gordon - Dennis Hopper