2. The Masters Of Evil
The Masters of Evil have many forms (some of which are impossible in the Marvel Cinematic Universe thanks to other studios having the rights to certain characters), but it is definitely in the Marvel Cinematic Universe that we are most likely to see an incarnation of these guys pop up. Loki, Red Skull, Abomination and various other supervillains are already established, while the likes of the Leader and Ultron have either been hinted at or are definitely on the way, so there is definitely scope for a formidable supervillain team to come together and challenge the Avengers. Ideally, the rights to Doctor Doom would be acquired by Marvel Studios in order to bring the greatest villain in comic book movie history to the best comic book movie franchise in history, but that seems unlikely, given his likely inclusion in the Fantastic Four reboot (we can dream though, right?). Regardless of the line-up, seeing a supervillain team come together in the same way we've watched the Avengers assemble would be cool as hell.