I'm going to have to say this:
StarCraft - OSTNot only because it sounds good, but because of the fact that the timing of the music is actually set to frame a typical game. This was made before games had the abiltity to change music on the fly depending on what was happening in the game, so when they crafted the soundtrack for this game, they timed the pacing based on the general times when action would pick up.
If you listen to most of the race music you'll notice it's pretty chill and calm until about 40 seconds in, which is when you only have your first workers. Then it starts to pick up a bit as your first buildings get constructed and generally first contact with the enemy is going to occur. Then it just does a steady pump as your forces build until it breaks into a full combat routine, which lasts about a minute or so before dying down again.
Essentially, the soundtrack is built around the flow of the game and I thought that was pretty amazing.
