I have to hand it to Epic Games they sure do know how to select music for their game trailers, especially Gears of War trailers. As seen in this, the latest Gears of War 3 trailer. The music from Mazzy Staradds certainly adds a mood that seems to fit the gears universe perfectly. Check it out.
http://www.youtube.com/watch?v=FE8vfZ5gCQg
If you want to listen to the whole song found in this trailer click here