Last rumor for the week, I think. Io9 has the rundown (which has what may end up being spoilers) on a rumor that The Dark Knight Rises will be based on Doeg Moench's Prey. That's not a story I've read personally, Moench does good work but I'm not a big fan of the gothic horror interpretation of Batman that he tends to go for. But the storyline matches with the rumors about Hugo Strange, a female villain, and another female character. So who knows? I agree completely, though, with Io9's take that if it is based on Prey, The Dark Knight Rises will bear only a passing resemblance to the source.
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.