Much like what happened to The Dark Knight Rises teaser trailer before it, somebody has camcorded and released the first trailer of Joss Whedon's epic film adaptation of "The Avengers", which is to be found as a post-credits scene at the end of "Captain America: The First Avenger". First detailed and described by a post in Superherohype, the trailer now finds its way into YouTube, and was featured up in Bleeding Cool along with screenshots. SPOILER obviously, so check it out below at your own risk and while it's still online, but sooner or later it's going to be taken down for sure.
UPDATE: The bootleg has been taken down. Wait til the official one comes out online, or watch it in theaters with Captain America: The First Avenger.
I'll leave descriptions and more info on the trailer above to be the source articles Superherohype and Bleeding Cool.
Captain America: The First Avenger arrives this July 22, while The Avengers assemble in theaters next year May 3!