The villain in Spiderman 4 has not been announced yet. But we are all trying to guess who it will be. I have been betting on the Lizard as being the most probable villain in the next Spiderman movie.
Some days ago I while searching for Spiderman 4 on the web I just found a video interview of Stan Lee, the creator of Spider-Man.
The interview dates back to one year ago. But I think it still sounds right and it would confirm the Lizard hypothesis:
Stan Lee Talks Spider-Man 4.
So Stan Lee asserted that:
I think unlikely that any producer or scriptwriter would counter Stan Lee's viewpoint.
So it's almost a given that the Lizard will be in Spiderman 4. Maybe the Lizard will join forces with some other villains to fight against the superhero Spiderman though.
Update as of 2009/03/16:
So Sam Raimi will stay faithful to the original source material. And I bet he will listen to Stan Lee: the old man is still the old man in the house! Quite sure we will have the Lizard by now!