Check this out, hot off the back end of an exciting weekend at San Diego Comic-Con 2010, lucky audiences were subjected to footage from both Thor and Captain America: The First Avenger. Check out the links below for each of the sites. Nothing much on them at the moment, but keep a close or register for updates to keep updated.
Captain America: The First Avenger is currently set for a release in July of 2011, with Thor in May of 2011. No details for Avengers just yet.
Nevertheless, just seeing those logos is ever so exciting.