Deus Ex, Halo and Mass Effect, I love their themes. I've got a full playlist of soundtracks, and half of that is from video games, and half of that is Mass Effect.
Deus Ex: HR and Mass Effect for sure, especially Mass Effect 3...best part of that game was Mansell's music.
If I had to add my own, Jeremy Soule's soundtrack for Guild Wars 2 is pretty fantastic too.