I thought Nolan wanted to translate the other Batman villains into film, i.e. the guys who haven't been on the silver screen: Mad Hatter, Clayface, Black Mask, Harley Quinn (who'd be so logical for the role in the third one), Killer Croc, and The Ventriloquist. We've seen Penguin, Joker (twice), Riddler, Two Face (twice), Catwoman, Bane, Mr. Freeze and Poison Ivy (though not done properly), Ra's al Ghul and Scarecrow. I think it's time for some others, though Depp as The Riddler would be so awesome if it were to happen.