First, let me go on record and say that a live-action Justice League movie should probably not involve Batman, since the newer films (Batman Begins, The Dark Knight)are much more reality-based, and maybe not Superman either, unless they manage to do another film and revamp the series like they did with Batman.
That being said, here's who I would use:
-Green Lantern: The leader of the team, and also one of the most powerful
-The Flash: Probably the Barry Allen version, although Wally West may appeal more to the kids
-Wonder Woman: The veteran of the team, and another powerhouse
- Martian Manhunter: The most powerful, and also the outsider of the team
- Aquaman: More likely the most recent version with the hook hand and long hair, just to make him more edgy
I guess Hawkman and The Atom could be added if they make a sequel, and the villain in the first movie would probably have to be Starro, just to keep with the continuity of the comic.