The soundtrack for The Social Network by Reznor and Ross is my staple. It's all instrumental with a good beat, and gets me in the entrepreneurial mindset.

Hand Covers Bruise: http://www.youtube.com/watch?v=9SBNCYkSceU

In Motion: http://www.youtube.com/watch?v=Yczul_609Gg&feature=relat...

Outside of that, anything techno-trance or industrial works. I definitely don't like too many voices, it's distracting.