If I'm writing in general (like now) I tend to listen to music that fits easily into the background and doesn't distract my focus. My playlist includes...
The Ghost Composer
Falling Water
The Very Best Of Enya
Come Away with Me
Jim Brickman: Beautiful World
If I have to write something a bit on the dark side, I opt for some pretty heavy classical stuff...
Mozart - Requiem / Augér, Bartoli, Cole, Pape, Wiener Phil., Solti
Wagner - Der Ring des Nibelungen (Ring Cycle) / Sir Georg Solti
If I am angry and venting I've gotta go for the metal hair bands and monster rock of the 80's...
Monster Ballads: Platinum Edition
Monster Ballads, Vol. 2
If I'm just plain moody, then I've got a playlist completely comprised of my favorite band (The Cure) to get me out of my funk and help me write more clearly...
Join the Dots: B-Sides & Rarities, 1978-2001
If I'm writing about strange subjects or sci fi, then I've gotta go with psychadelic rock. Pink Floyd is the obvious here, but my playlist also includes King Crimson...
Discipline
If my writing needs to be more spiritual in nature, I will listen to rhythmic drumming...
Drum Circle
Of course, I have about 50 different playlists for writing. If you've got an iPod full of music, why not create a few mood enhancing playlists of your own to listen to while you write? Let me know what you're listening to... it just might make it on to one of my lists as well.