I have seen a few post on the Gears of War trailer. I have also seen a few people ask about the music in the trailer. The song, as you probably all ready guessed, is titled Mad World. The song was originally written and performed by Tears for Fears. The version used in the trailer is performed by Gary Jules. This is the one I prefer ever since I heard it on the Donny Darko sound track.
The Gary Jules Version
The Gears of War Trailor
The Gary Jules Version
The Gears of War Trailor