The Joker and Two-Face have definitely been done before. I think Nolan could pull off The Riddler with the right actor, but I don't know if Catwoman would fit. I mean let's face it, her character is nowhere near as interesting as the others we've seen. So far Nolan's characters have been heavily influenced by different codes of morality. I just don't see Catwoman as being that deep of a character. She steals, she likes cats, she's good looking. I suppose Nolan could build her up as more of an anti-hero, but as an anti-villian, she can't compete with Ras or Two-Face. The Riddler, however, is perfect for creating a deep and intricate character.