Thought they’d wait for AFTER “Iron Man 2” for this, but here we are: Yahoo has the first still of Chris Hemsworth in costume as The Mighty Thor:
http://movies.yahoo.com/photos/movie-stills/gallery/2588/thor-stills#photo0
(there’s no copy-n-paste-able version yet)

The chief advantage that Marvel Films has over anyone else making superhero movies is that Marvel has been doing NOTHING BUT selling superheroes to people for almost SEVEN DECADES now, meaning that they know “what you need to get right” like the back of their hand. Q: “What does Iron Man need to look like?” A: “Red and yellow, with Gradnov’s mecha-design but retro-fitted to more-closely resemble the 70s/80s armor.” Bingo. Q: “What does Hulk NEED to have?” A: “Purple pants, the green eyes and sad walking away music from the TV Show and another monster to fight.”

Q: “What will tell fans that Thor is going to be THOR?” A: “Red cape, circular metal plates on the tunic, the beard from Simonson’s run, the plated-mail on the arms from Stracyzinski’s run.” Done. (betcha beard/no-beard is how they distinguish between Thor/Donald Blake, too.)

What’s cool is, Thor is the superhero for whom costume-accuracy matters LEAST – a Viking flying around in modern times hitting stuff with a magic hammer is going to look like Thor regardless of the details… so it’s really something that in this pic Chris Hemsworth basically looks like he’s wearing the world’s most expensive Comic-Con Cosplay. Well done.