Oh there are too many to choose.
I always have been partial to Marty O'donnell's work (Bungie games). Every soundtrack from the Halo series is beautiful and there are no words to describe Siege of Madrigal (Myth series)
Bastion's soundtrack completely blew me away. Mother, I'm here, Build that wall, and Setting sail are all in my top five video game songs. The rest of the soundtrack is not that far behind.
The soundtrack from Mirrors Edge was awesome and Still Alive is probably what got me to buy that game in the first place, I just wish the game lived up to the hype. I still had fun in it but it had so much more potential.
Almost every single song in the Sonic Adventure series. I grew up on those games and Crush 40 will forever be the king of sonic music in my eyes. I can appreciate the 2d games and the bit music present in them but I'll take Metal Harbor over Chemical Plant any day.