Despite a casting call that went out last week asking actors to read for parts in the Fantastic Four sequel that specifically mentioned Galactus and Silver Surfer would the villains of the movie, another source disputes that story.
Comics Continuum says it talked to sources that said that report was "inaccurate." Director Tim Story has said that Doctor Doom would return (whether he's played by Julian McMahon or not is still up in the air) but that wouldn't preclude a Galactus/Silver Surfer storyline. Doom has tried many times in the comics to steal the Power Cosmic from these two beings.