Starcraft, my favorite real time strategy game and arguably the best ever made. The first one had some freaking awesome music! I'm not a fan of the soundtrack of the sequel though.
I think what made the music so good in the first one is that it was so influenced by the Warcraft 2 soundtrack. Indeed, the song used in Starcraft 1 are electronic covers of more warcraft-ish orchestral pieces that were originally intended for the game. Here's an example (see if you can recognize some of the songs in there):