Depends on what I'm doing. If I'm working on plotting something out I'll put together a soundtrack mix to help visualize what I want to go on. I've got ~20,000 tracks in my iTunes library (I might be a bit obsessive) ranging everywhere from Bach to Eminem, so I'll throw together a mix on a song-per-scene basis. That works for plotting and imagining. When I'm getting down to the actual business of writing I prefer something high-energy and long-running, so I'll end up throwing whatever that week's Eminence United podcast is on and letting the trance drive my keyboard.
Mr. Fnord interdimensional man of mystery
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"I. Drink. Your. NERDRAGE!"
Mr. Fnord interdimensional man of mystery
FenWiki - Your One-Stop Shop for Fenspace Information
"I. Drink. Your. NERDRAGE!"