The SimCity4 soundtrack is really awesome for just hacking away at things. I think that the Red Alert soundtrack is one of the best "get shit done" albums I've had in my box for a while, even with the amazingly cheesy synths and 90s style. The Descent and System Shock 2 soundtracks were very much in this vein (SS1 was procedurally generated, so it's hit or miss).
I think the big trick is that game music is meant to get you thinking and active, but not distract you.
I think the big trick is that game music is meant to get you thinking and active, but not distract you.