That trailer for "The Social Network," otherwise known as "The Facebook Movie," is dead-on brilliant. The scenes tell just enough of the story without making you feel like you've seen it all, Jesse Eisenberg is an eerie Mark Zuckerberg, and of course, that song, overlaying it all.
That song is Radiohead's "Creep" (link to original version here) as done by a Belgian women's choir. EW has the info, and a full version of just the song.
"Creep" itself has an intriguing and complicated history, which you can read about here.