io9.com has a list of 5 villains they want to see.
The poll for who should play the Penguin is now closed. Paul Giamatti was the clear winner, followed by Bob Hoskins. Philip Seymour Hoffman, often rumored to be playing Mr. Cobblepot, tied with "someone else." This week: Catwoman poll. Vote on the right side of the page. And, as always, any suggested villains to look at should be left in the comments.
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.