I'm more of a DC guy than a Marvel guy so...
Captain Marvel. It'd have to maintain a lighter style than Nolan's and could be hard to pull off considering the problems with his name and the comic book cheesiness of his look and most of his villains. They made an excellent animated feature with Superman a while back, though. Though Mr. Tawny pretending to be a hobo to test Billy's character was slightly weird.
Aquaman. Get Geoff Johns on the movie and give him editorial control and it'll be awesome. The man writes Aquaman beautifully.
Doctor Fate. Screw the Sorceror Supreme, the Lord of Order is where it's at. There'd have to be an adaption of elements of his backstory (discussions of Order, Chaos & Balance probably wouldn't be that entertaining for movie-goers), but he's got a decent selection of villains plus other magical villains in DC that could be brought in.
Hawkman & Hawkwoman. Call her Hawkgirl if you want, but I would blood-eagle Marvel executives for DC if they could do this. With the Golden Age back-story, as well. I've always felt the two iterations could have been easily seperated with some decent editing.