Taking a week-ish long break from villains to talk about some characters friendly to Batman who might pop up, starting with the original Robin.
Probably the best known origin of anyone in Gotham other than Batman, Dick Grayson grew up in the circus as a member of the acrobatic Flying Graysons. While still just a boy, Dick saw his parents murdered by mobster Tony Zucco. Having suffered through the same thing as a boy, Bruce Wayne takes Dick Grayson on as a ward, and when Dick discovers Bruce's secret identity as Batman, Dick becomes his sidekick Robin, the Boy Wonder.
Pros: Out of all the Robins, Dick is the most famous. So much so that any other Robin would probably confuse fans who associate Robin with Chris O'Donnell or Burt Ward. The acrobat backstory provides an excuse for his agility and fearlessness.
Cons: First, and I'm probably going to mention this in every Robin, we're already pretty sure there won't be a Robin, and Robin is a tough sell anyway. In a semi-realistic interpretation of Batman, it's hard to justify putting a kid in that kind of danger.
Second, there's the short pants. He's a kid, and the costume was designed almost 70 years ago, so I can't blame Bob Kane/Bill Finger, but it's not a good look.
Third, and this is a personal opinion, he's a little bit boring. At least as Robin. He rarely seemed to challenge Batman and almost never did anything on his own. He was just an occasionally wisecracking kid who did flips, kicked people, and got taken hostage.
How I'd do it: I'm going to save this until after I've covered the three (major) Robins, since I'd include elements of at least two of them.
Casting Guesses: Who knows with kids, but I'm sure it'd be a long, difficult casting process.
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.