Wanderingbert on flickr is undertaking the Batman Villain Project, where he intends "to draw as many batman villains as possible. Even the obscure and mostly unknown ones. And even the dumb ones that may look interesting but suck as actual villains. Even them." Pictured above is one of "them," Doctor Phosphorus.
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.