Won't be Stromm, I doubt they'd adapt the Clone Saga since it's getting plenty of hate for not having Spiderman be a 50 year old pastiche of a geek, Electro seems unlikely since they seem to at least be following a theme of genetic manipulation enhancement etc (seriously, played the game first and the movie at least follows a good line thematically, not that Bob's gonna accept that line of reasoning), I... kinda want to say Chameleon too but not sure. Cos Morbius would be cool, but it'd just make the Twilight comparisons more justified.
It depends on the line they take after this, I doubt they're going to have serious plot revelations in the second movie and the third's going to be "Catch your Girlfriend, Spiderman" with an amped up Osborn so... if Sony have the balls to kill Gwen off that'd be an interesting third movie. More interesting if they find actual goblin DNA to cross Osborn with, even if it'd jump the shark.