I can’t really single one out, but out of all the upcoming Marvel movies, I may be looking forward to Thor the most.
Don’t get me wrong, I want The Avengers movie and the Captain America: The First Avenger movies both to be awesome, but Thor, I think will be trickier to pull off.
It looks like they are going with the Jack Kirby and Walt Simonson vision with the huge cathedrals and almost a sci fi / fantasy look.
Which I think is great.

http://comic-kingdom.blogspot.com/2010/09/upcoming-marvel-movies-thor.html