Cornelius Stirk likes to eat people's hearts. But he finds that they're tastiest when flavored with "fight or flight" hormones like norepinephrine, so he likes to scare the bejeezus out of them before they die. He has a "hypnotic aura" that lets him make people see him as anyone he wants, which helps him gain people's trust and get close to him (in a few stories, he has used the image of Abe Lincoln), and it also helps with the scaring part (though his natural face is already pretty frightening).
During Knightfall, Stirk teams up with the Joker and they kidnap Commissioner Gordon. Stirk uses his abilities to appear to be Batman and mercilessly tortures the Commissioner. Batman, of course, saves the day, eventually, but Stirk's treatment left Gordon awfully shaken up.
Pros: Abe Lincoln is always funny. And he's a nice contrast to Batman, who is out to do good but projects a terrifying image, while Stirk is out to kill but projects an image to put his victims at ease before he strikes.
Cons: He's a little bit too much like Scarecrow with the whole fear thing, except with supernatural powers that would be hard to believe. And killing people and eating their hearts is a little much for a PG-13 movie, I think.
How I'd do it: His original introduction was when someone was found murdered, and had been seen earlier that night at a bar, talking to a guy who looked like Lincoln. I liked that. I guess I'd rather have him be a master of disguise, disfigured under his masks/makeup, who puts on trustworthy faces to get close to his victims. And I guess keep the heart eating thing, but figure out how to do it with heavy implications but not actually showing it.
Casting Guesses: An unknown. Usually movies where a famous actor is a "master of disguise", we're so familiar with their voice and face that even in an elaborate latex mask, they just seem like the movie star we know in a latex mask. An unknown would be a blank slate, and could actually fool us.
Verdict: I can't see it happening, it's mostly the Scarecrow thing, but he's also not a high profile villain at all, and he'd take some reworking to deal with his supernatural powers.
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.