It takes time to "train" Pandora but I've been at it for 3-4 years now seeding with all the tracks that are great for coding and thumbing up when I hear something that promotes going in to zen mode. The results are great and now this is my favorite music source in everything else I've tried out: http://www.pandora.com/station/play/164715539305919382. The status features mostly vocal-free distraction less music with rhythmic beats that puts you in the zone and occasional uplifting tracks that keeps you going.

I've also found this music station to be very anti-procrastinating. If you feel like procrastating, just press the play button and suddenly you would want to get back to coding :).