There was a rumor today that Joseph Gordon-Levitt would be playing Alberto Falcone (a major character in The Long Halloween) in The Dark Knight Rises, but the rumor was started by someone at IGN speculating at a role JGL could play, which people then took to mean that he had inside info (the article at slashfilm has this tidbit as an "update" buried in the middle for some reason).
After The Scarecrow, Ra's Al Ghul, The Joker, and Two-Face, who should be Batman's next enemy in the Batman Begins/The Dark Knight series? Well, as of now we know that Tom Hardy will play Bane and Anne Hathaway will play Catwoman.
Check out the master list for all the villains covered. I've pretty much run out by now. Obviously, there are more Batman villains, but not any of significance that I know of. As of February 2009, no one is confirmed as a villain. Not the Johnny Depp Riddler, not Phillip Seymour Hoffman Penguin, nobody.