The Ain't It Cool article is right on, in terms of taking any rumored casting seriously. I link to rumors and talk about them, but they really don't mean a thing. Adrian Brody and Paul Bettany were the big rumors circling for the Joker, and we know how accurate they were. So when I talk about Angelina Jolie as Catwoman or Johnny Depp as the Riddler, it's just for the fun of imagining them in the part (and also because this blog has a very narrow focus and I'll run out of material if I do nothing but plow through villains).
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.