Above, a clever fan-made Riddler poster from millarc (click the image for a larger version if you can't read it).
I was behind on my reading from having just moved, but MTV's Splash Page was super busy with Batman-related stuff over the past couple weeks. They held a poll on which villain should appear in Batman 3, and their readers chose the Riddler. And in an interview with Dane Cook, he said he wants to play the Riddler, which should never happen.
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.