As the world's greatest detective, Batman doesn't always show much respect for other detectives. Although he occasionally consults with other detectives like The Elongated Man or Bobo the Detective Chimp, Jason Bard is the only detective I can think of that Batman has ever actually hired.
A former Gotham City cop who was wounded in the line of duty by Killer Moth. He quit the force and opened up his own business as a private investigator. Around the same time, he started dating his former boss's daughter, Barbara Gordon. They were pretty serious, but after Barbara was attacked by the Joker, she left him. He reappeared years later when Barbara was running the Birds of Prey, and he was actually temporarily blinded in an accident while helping out her team, but he wasn't able to rekindle his relationship with Barbara.
His relationship with Batman would begin after all this, when Batman was concerned that Harvey Dent, who had been reformed, had lost his way. Having been absent from Gotham, there wasn't enough time for Batman to chase all his leads, so he hired Jason to investigate the disappearance of Orca.
Pros: The movies have played up the physical and psychological aspects of Batman, but haven't paid much attention to his skills as a detective. Including Jason Bard in the third movie would certainly push the story in that direction.
Cons: Jason would take the focus away from Batman and whoever the central villain of the movie might be. Plus, it really wouldn't sell Batman's detective skills very well if the first time he really needed them in a movie, he had to hire someone else to assist.
How I'd do it: Nothing too fancy, just have something that needs investigating during daylight hours, maybe have a scene where Bruce Wayne tries to look into it, but he's too recognizable out of costume to accomplish anything, so he hires Bard.
Casting Guesses: James Marsden. He looks sorta like Jason Bard, and has the right personality too.
Verdict: I doubt it. But if there is a private eye somewhere in Batman 3, they might just name him Jason Bard to pander to fans, but I can't imagine much time spent on a Jason Bard character.
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.