The Batman 3 rumor mill came to a halt after Gary Oldman's surprising (and unconfirmed) announcement at the San Diego Comic Con that filming would begin next year. Well, there was word that Miley Cyrus wants to be Batgirl, but I can't see that happening.
It could also be Bette Kane, who many many years ago was "Bat-Girl", the sidekick to Batwoman. Those stories were written out of continuity, but Batwoman has recently been reintroduced, and is currently starring in the beautifully drawn pages of Detective Comics, so bringing back Bette Kane is not out of the realm of possibilities.
But none of these characters I mentioned, with the possible exception of Babs Gordon, will be appearing in a Batman movie any time soon, so this is only of interest to hard core Batman nerds, like me.
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.