Dr. Karl Hellfern was the first recurring villain and first real supervillain to face Batman in the comic books. In his first appearance (nice article about that here), he threatens Gotham City's wealthiest citizens with a toxic gas unless they pay him a hefty sum. He's been reinventied as a paraplegic with the same poison gas gimmick, and more recently as biological and chemical weapons expert for sale to the highest terrorist bidder.
Pros: He's a blank slate. Doctor Death is a name some comics fans know for his historical significance, but few have read much of anything featuring the character. So there's plenty of freedom to update or make changes to the character.
Cons: The name "Doctor Death" these days makes most people think of Jack Kevorkian. No matter what your opinion on doctor assisted suicide, I think you'll agree it's not a great thing for people to be thinking about during your blockbuster action movie.
How I'd do it: I might avoid the Doctor Death name, let people call him that in discussion on the internet and stuff, but I'm not sure you really have to use the name in the movie. I feel like this has been done before in a movie, but the closest example I can think of is that I'm pretty sure they never used the word "Bizarro" for the evil duplicate of Clark on Smallville. As for the story, I can't really expect him to be the main villain, but he could be a secondary guy. Maybe criminals in Gotham are sick of Dr. Crane's fear toxin, but do like the whole toxin idea, so they go to another crazy scientist? That's probably a stretch. But these movie writers are far more clever than I am.
Casting Guesses: The only depictions of Doctor Death I remember all have him as a balding guy with a beard. And I like the idea of a creepy old guy. So Joel Grey, or Ron Rifkin?
Verdict: Possible. Like many others, Doctor Death has little chance of being the main villain, but he's a perfectly decent character and could be used if the story calls for it.
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.