1. Andy Serkis as The Mad Hatter
2. The Riddler being the central villain, not a serial killer or anything like that. But an ambitious con-man planning a huge robbery of some sort. Have him playing both the police and the criminals. Also, I want to see him have an evolving costume. Showing him becoming the character we all know from the comics.
3. The Penguin. Not of this "realism" bollocks either, he's a great character. What's unrealistic about him? He's a mobster, he plays up to a certain image, he has trick umbrellas. Nothing outlandish about that.