Renee Montoya, like Harley Quinn, was created for the 1992 Batman Animated Series, and worked well enough to cross over into the comics. For a little bit, I thought Montoya had actually been written into The Dark Knight, since there was a hispanic woman working on Gordon's team, but it turned out to be Anna Ramirez.
For many years, Montoya was partnered with Harvey Bullock, a Gotham City PD detective who's been in the comics since the 70s. His traditional tough cop who goes by his gut played well off of her more modern, educated, analytical style (though she certainly is tough as well). They both learned from each other and seemed to become very close. Eventually, Bullock was promoted and Renee then partnered with Crispus Allen, a detective from Metropolis who isn't used to the kind of rule bending that is more common in Gotham.
Further on down the line, Two-Face becomes infatuated with her, finds out she's a lesbian, and threatens to out her. Allen ended up being killed, Renee then resigns from the force and becomes The Question (taking over from original Question, Vic Sage, on whom Rorschach from Watchmen was based), and she starts up a relationship with Kate Kane, aka BatWoman.
Pros: Other than Gordon, the Gotham cops have been pretty awful people, so it'd be nice to have another good one. And she's an interesting character in general.
Cons: Sad to say, but having another Latina on the force might get people her mixed up with Ramirez.
How I'd do it: No real secret to this, just make her one of the cops.
Casting Guesses: I hate to say it, because she doesn't seem like the greatest person in the world after her stint on Lost, but Michelle Rodriguez would make a pretty good Renee Montoya. I haven't watched much of Life, but Sarah Shahi might not be too bad either, although she almost looks too pretty or too small or something.
Verdict: Like most any cop that's been a regular in the comics, she'd be a great fit.
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.