Screen capture of the last image in Iron Man 2. SHIELD Agent Coulson phones Fury to tell him, "We've found it." Too spoiler-y? Tough. You had your chance to see the movie early if it mattered that much to you. I've been sitting on this photo for weeks.
Yes, that is the Mjolner, hammer of the Mighty Thor. And interestingly, it looks very much like it did in the original comic books, and not in the updated Ultimates universe.
The hammer find ties into several cryptic comments made during the film about SHIELD's other priorities and missions. Although he doesn't come right out and say it, Nick Fury seems to hint that he's been around a long, long time. Long enough to know Tony Stark's father Howard. Long enough that he'll appear in the Captain America movie? Who knows? I do know io9 reported that the actor who plays Howard Stark was hired to reprise the role in Captain America.
BTW, any guesses just what the Avengers Initiative really is? Obviously it's an excuse to put Cap, Thor, and Iron Man in the same movie. But just what is the catalyst the initiative is meant to address? Could it be a secret Skrull invasion?
The Mighty Thor is set to release May 2011, and Cap appears in July 2011, with an Avengers movie set for May 2012 -- so we will at least get all the movies prior to the Mayan apocalypse striking us.