Re: What villains are left for a 4th film?
Hmmm...I'm sure with all their tentaclely goodness the Quintessons would be a good villain if you pair them up with Unicron.
"You're not just anyone. One day, you're going to have to make a choice. You have to decide what kind of man you want to grow up to be. Whoever that man is, good character or bad, it's going to change the world." - Jonathan Kent, Man Of Steel
*sarcasm* It's nice to know that some people know what's going with me when I don't. *sarcasm*