For each of my completed works, I've done something somewhere that's been influenced by a choice in music. Mainly I listen to music from video games. That's partly because movie or television/anime music tends to be slightly more specific than game music, classical music has different associations for me and so isn't very helpful, and popular music is just distracting. As for video game music, its great variety, prolific history and looping nature make it perfect for prolonged mood setting and general help.
For The Leviathan Chronicle, the medieval setting is something that can be difficult to find, as true medieval music encourages listening more than working (believe me, I've tried). So I went for some other things that would help evoke the right setting. Final Fantasy Tactics and Vagrant Story provided invaluable mood music when writing about the book's mature subject matter. Its more sacred moments were helped along with a liberal dose of Gregorian chant music from one of my father's CDs and some pieces from El Shaddai: Ascension of the Metatron and Shadow of the Colossus. Mostly not very ancient, but all highly emotive and somber.
For Stella: Maiden of the Dusk, an in-progress project which may or may not see the light of day, I went in a different direction. My influence drew from anime, particularly the work of Joe Hisaishi for Princess Mononoke and Nausicaä of the Valley of the Wind, and the pieces created by Naoki Sato for Production I.G's Blood-C. I was actually inspired by those two anime to create something of a post-apocalyptic zombie-style tale with romance and a strong grounding in Mesoamerican and South American folklore. I also used the available musical pieces from Final Fantasy XV (nee Versus XIII), as I'd imagined my heroine as a tribute to that long-lost figure of fan fiction and dreamy-eyed nostalga Stella Nox Fleuret. Yes, I called her Stella, but then lots of heroines are called Stella, and otherwise she's nothing like Nox Fleuret. She's certainly got better tastes in shoe heels.