Joss Whedon's The Avengers is a true phenomenon. Thanks to its success, a whole pantheon of heroes who spent decades in relative public obscurity, outshone by the likes of Batman, Superman and Spider-Man, now have their faces plastered on action figures, t-shirts and fast food soda cups. And to his credit, Whedon made an incredible film. The Avengers is everything a superhero flick ought to be. It contains plenty of humor, has outrageous special effects and shows titanic men and women battling incomprehensible evil. Far from the broody, gothic realism of Christopher Nolan's Batman movies, the Avengers makes no attempt at tricking you into believing its outrageous scenes could actually happen here. When it's over, everyone can go home and talk about how much fun they had. And Marvel's cinematic roller coaster shows no signs of slowing down. Iron Man 3, the first film of Phase Two, received poorer reviews than many of the Phase One films did but still smashed the box office. The new Thor is due out in September and Captain America: The Winter Soldier follows in 2014. But all of it leads up to The Avengers 2 and everybody wants to know which new characters will be introduced in those sequels. There are plenty to choose from. In the comics, the team's lineup changed routinely. Many iconic Avengers did not make the first film. The Marvel Universe is chock-full of guest stars and superheroes who could easily make one-off appearances and there are many who could be added to the permanent roster. These are 10 characters worthy of inclusion in a future Avengers sequel. Hopefully the franchise goes on long enough that we'll get to see them all.