Classical music is ok, but I find I either drift off or work too slow with it. Contemporary classical music is a bit better - esp. something with a chilled out mellow beat.
The sound track to the film Great Expectations is a good one. I'm quite productive with this one...erm...with my work that is :$
Muse is another really good one. On the other hand, maybe not. I always end up getting caught in the lyrics, just sitting there listening and analysing them. Oh man I love Muse. Muse, if you're out there somewhere (maybe doing a Phd...), You're POWERFUL :-s . So awesomely great that I think I will award you with another constipated look... :-s
If all that doesn't take your fancy, how about taking a little break and and press the play button to:
Queen - The Show Must Go On