I don't have specific music for each book. My music varies by my mood. My main listening choices? Celtic folk, Celtic punk, Jimmy Buffett, Warren Zevon, and a diverse group of other odds and ends. I guess if I'm doing a paranormal, I might lean more to the Celtic, while with a western, I might lean more to the Buffett and Eagles. Maybe. The Buffett also tends to come out when I'm sick of winter in Michigan. Zevon gets played when I'm disgusted with the world. Grateful Dead when I'm feeling old. Great Big Sea is for--well--practically anytime. I DO usually have music on when I write--that or the TV on something like game shows or travel channel--basically something in the background I can ignore. I have trouble writing in dead silence.
One quirk? The faster the music, the faster I tend to type, if I'm in the zone. So if I'm smart, it's the dh's punk albums that are on my MP3 player, or in the CD changer. I also use Pandora and Last FM, two internet radio sites that are easy to manage without looking up from my computer.
My youngest son once told me, "Mom, you never did near enough drugs to account for the music you listen to." You know what? The kid is right.