Director Sam Raimi has been talking about Spiderman 4 in an interview given to MTV (here), and here the most interesting tidbit:
So they dugg into the precious history of Spider-Man comic books in order to select the right villain(s) for Spiderman 4. Well, I’m quite sure that the Lizard will finally get his part, even Stan Lee wants the Lizard in Spiderman 4! And if Sony and Sam Raimi insist to bring in one more villain, my bet would be on Morbius the living vampire.
By the way, Spiderman 4 is scheduled to be released on May 6, 2011. Tobey Maguire will of course reprise his role as Peter Parker aka Spiderman, and Kirsten Dunst is more than likely to be proposed her role back (the old Sam Raimi has indeed a crush on her).