This is, indeed, the very last bit of Captain America: The First Avenger. A movie that came out less than a week ago. Here's the end of it. Online. Apparently sanctioned by the studio, considering it's a Yahoo site and it's obviously not some in-theater camera bit, and the post-credit sequence is edited in as a shortened teaser for what you'll get if you go to see it in theaters.
I don't get it, either; why edit down the teaser for The Avengers but make it about as long as the actual teaser in the post-credits sequence is? Why give away the final scene of the film at the same time? Do they just expect that everyone who's going to see it will have already done so by now? I guess we'll go ahead and post them embed since Marvel seems to be cool with it, but...yeah. Color me confused.