Just for the heck of it I thought I would give my guess as to who the next Spider-man movie villain will be.
My official guess is... Maxwell Dillon "Electro"!!
He is an early villain, 1st Appearing back in Feb of 1964 in Amazing Spider-man #9.
Thomas Haden Church was recently cast as the major villain in Spider-man 3 and honestly he really looks like an Electro.
Althought Sam Raimi isnt saying who the next villain will be he does say this:
“...we wanted to have a villain not only who would fulfill the character needs but somebody who could entertain the audience on a visceral level and provide great visuals, something we haven’t seen before, and create a real challenge and great foe for Spider-Man and his unique spidery, spider-like powers,”
Electro would certainly accomplish that, and I can’t think right now of another core Spidey villain that could.
I’ve read where some people want Venom to be the villain, but that would be ridiculous. Having Venom in the movie would make no sense at all.
It’s not been announced yet, but Electro is who I am guessing it is. He just makes sense. We’ll see if I am right.
Above is the cover of Marvel Knights Spider-man #2 - If it’s electro as the next villain then everyone on that cover with the exception of The Vulture will have been in a Spider-man movie.

The Cover of Amazing Spider-man #9 - The first appearance and Origin of Electro