As with most major projects the release dates have been moved out, but here's the latest on casting etc. They're going young, apparently so they can have spinoffs & sequels past the dates where Christian Bale etc. will be too old to play the characters.
Justice League of America (2010)
Director: George Miller (Happy Feet, Witches of Eastwick, Mad Max series, Lorenzo's Oil)
Screenplay: Kieren Muroney, Michele Mulroney
Cast (rumored, but likely)
Superman/Clark Kent: D. J. Cotrona
Batman/Bruce Wayne: Arnie Hammer
Wonder Woman/Diana: Megan Gale
The Flash/Wally West: Adam Brody
Green Lantern/John Stewart: Common
Talia al-Ghul (Ra's daughter): Teresa Palmer
????: Zoe Kazan
Justice League of America (2010)
Director: George Miller (Happy Feet, Witches of Eastwick, Mad Max series, Lorenzo's Oil)
Screenplay: Kieren Muroney, Michele Mulroney
Cast (rumored, but likely)
Superman/Clark Kent: D. J. Cotrona
Batman/Bruce Wayne: Arnie Hammer
Wonder Woman/Diana: Megan Gale
The Flash/Wally West: Adam Brody
Green Lantern/John Stewart: Common
Talia al-Ghul (Ra's daughter): Teresa Palmer
????: Zoe Kazan