Probably all his villains, next to Batman he has one of the greatest rogues gallery ever.
One of the reason I love spider man and batman a lot because like they say a hero is only has good has his greatest villains or something like that. I wouldn't mind seeing the spot in a movie has I think he would make for some interesting fights. My favorite villain that has yet to be used is carnage but we would need venom first. Other then that my favorite to have not been used in a sm movie yet would be shocker and hydore man. I don't know if they would use hydore man because he is kind of like sandman but I gusse you could say shocker is kind of like electro to.
Wouldn't mid seeing Hydro Man and Sandman combine to create the mud monster like in the comics, I got a feeling we will see Carnage in the next few years. Vulture is a character I would like to see on the screen.
I didn't know about the mud monster thing you said has I never really read the comics more just watched the movies and cartoons and played some of the video games. I don't want to see vulture in less there is at least one other villain has vulture is one of spider man worse villains and I don't think he can cary a movie by him self.