I wasn't sure if we'd get one after the lackluster opening of the first Avengers movie, but it has been official. No release date as of yet. Iron Man 3 and Thor 2 are both 2013 and Captain America 2014, so I'm guessing Avengers for 2015, but that's only a guess.
http://www.hollywoodreporter.com/news/disney-avengers-2-bob-iger-iron-man-thor-captain-america-321670
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and then if that doesnt work look for the conclusion to the John Carter: Warlord of Mars trilogy with the final instalation...
"Ja"
@Michael777 mentions Nova (which would be KILLER), but I'm thinking Mar-Vel is probably more likely.
Introduced in Thor 2?
Interstellar threat: Check!
Playing on the well-established fact that nobody else can lift the hammer: Check!
Taking advantage of the "Two" in the title: Check!