Sci-Fi Wire has the details about the film, but it looks like Michael Chiklis (The Shield) will play Ben Grimm, Ioan Gruffudd (King Arthur, Horatio Hornblower), Reed Richards, and Chris Evans (Not Another Teen Movie) as Johnny Storm.
Jessica Alba (Dark Angel, Sin City) is the front-runner to play Sue Richards.
Note: I’m guessing at the Chris Evans mentioned in the article. There are four actors with that name in IMDB. The one I picked best matches the age needed for the role. Anyone have any better data, please post it.