Maybe they're going to do a Hobgoblin/Green Goblin thing. They could fool a lot of the fans by teasing Hobgoblin as the main villian, just to have him as a "copycat criminal" zipping around for a little while in the movie until Harry shows up in the Green Goblin costume and gets rid of him, before moving on to the main event with Spider-Man.
I hope it's not Sandman, that seems like a pretty weak alternative when they have several more interesting characters they could go to before him.
And this bit is from nearly a decade ago, but I remember Marvel was all hung up on doing a Venom movie independent of the Spider-Man films...of course, this was from back when the Spider-Man movie was still tied up in legal problems that prevented it from being made, so I'm sure a lot of plans have changed since then. I don't think Venom has enough support from comic fans, nor the recognition factor from the general public at this point to carry an entire movie.
I'm so tempted to see Virginia. I had a contentious thing happen with that being a film that got an opportunity my film didn't get, and it looks HORRIBLE. 4% on Rotten Tomatoes. 5.something on imdb, etc. etc.