It's been announced that Topher Grace has joined the cast of Spider-Man 3. The powers that be are keeping hush hush about what role Topher will be playing, only saying that he is perfect for the role they've chosen.
They have been equally secretive about the role which Thomas Hayden Church will be playing. They announced a while back that he would be playing a villain in the film, but have yet to announce which villain. Much of the online speculation has been that he will appear as Sandman, but no one truly knows for sure yet (no matter how much the fanboys insist that they know).
Some sites are reporting that Topher will also be playing a villain, yet there has been no official announcement of this being the case. He joins returning cast members Tobey McGuire, Kirsten Dunst & James Franco.