Now, although [Sinister Six](movie:1274281) , due to the Marvel-Sony agreement, isn't confirmed, I just want to share my idea out to everyone. So here we go...
Almost always the leader of the team, Doc Ock is a must if Marvel makes this movie. I also think it'd be cool if they were able to bring Alfred Molina back into the role.
I am truly shocked that neither Webb nor Raimi have chosen Mysterio to be a main villain. I mean, come on, just look at his his awesome mask! With good special effects and a good actor, Mysterio could shine.
Kraven the Hunter
A merciless villain who wants nothing more than to see Spider-man's head in his trophy wall.
Another mainstay of the comics team, the Vulture is an awesome villain who could lead to some awesome action scenes on the big screen.
Scorpion is an interesting villain because what he lacks in brain, he more than makes up for in brawn.
Now, I know that this is an unorthodox choice, but I firmly believe that Bullseye would be perfect for the Sinister Six. I feel like he would be perfect.