Look at that poster again... above Thor is that a wormhole he's creating?
No, it can't be a tornado as it doesn't really look like the tornado he created in Thor.
What do I think? Well, I think that Thor hears that Loki is on Earth and is afraid he'll cause damage on there, so he might have someone make his hammer be able to create wormholes to other dimensions.
This would make sense of how he gets to earth as it would be silly to have Nick Fury use the cosmic cube to open a wormhole to Asgard and tell Thor, "Awesome place to hang your helmet, by the way my name is Nick Fury director of Shield, and I'd like to talk to you about the Avenger Initiative."
(By the way this is just to be funny... sorry I can't think of another way he could get to Earth but I would be glad to hear any ideas.)
At any rate this is one of the things I'm most curious about in Avengers. What do you guys think?
The Avengers smash into theaters May 4 2012!