It turns out that as reported here, the Justice League of America movie has been put on hold - at least until June 2008. IESB.net has a source involved with the pre-production of the film in Australia, who says that the word has come down to officially put the film on hold.
Their source says that Justice League of America will be put on hold until the WGA strike is completed at the earliest. Last week, the crew was told to prepare for the worst in terms of the future of the film, and it seems the worst has come to past.
Officially, Justice League of America has not been cancelled, just delayed. However, it is certainly possible that the film will end up in limbo indefinitely.
Justice League of America would have combined the greatest heroes from DC Comics, including Superman, Batman, Wonder Woman, Green Lantern, the Flash and the Martian Manhunter, all in one film. Casting rumors for the film have run rampant over the past few months, although at this time Warner Bros. has still not officially confirmed any of the actors who had been offered roles in the film.