4. Peter Petrelli (Heroes)
Peter can copy the powers of any super-powered individuals in his vicinity. There havent been any characters like Peter in superhero movies. We've seen most powers used before and we tend to know which powers each character possesses and that comes with an element of predictability when it comes to guessing what they might do next. Hulk is always going to use his super-strength, Thor is always going to generate lightning and Loki is always going to create illusions. With Peter, you would never know what super-power he was going to use next, because he could choose to use the powers of any heroes or villains who happened to be nearby. For that reason, I think it would be great to see him in the Avengers (despite the fact that he was very, very annoying).