There's been a lot of talk about the future franchise of Superman being pushed towards a Justice League of America film which would also bring in other heroes like Flash and Wonder Woman helping to lauch their own stand alone films.
Recently IESB.net has reported that a script for JLA has been well received by Warner Bros. and they'd like to push it forward in early '08 going into production in Feburary/March to have a film done for a 2009 summer release.
They're team also confirmed that the JLA would likely consist of Superman (Clark Kent), Batman (Bruce Wayne), Wonder Woman (Princess Diana), The Flash (Barry Allen), Aquaman and the Green Lantern (John Stewart) and will follow the OMAC storyline and also feature Maxwell Lord.