I love music, and I love making lists, so making playlists is a huge timewaster pleasure for me. Unfortunately, one of the things I've realized with time is that I can't listen to anything while I'm writing. I need either white noise or no noise. It's sad, not even instrumental/classical music makes the cut. I get sucked in and can't do anything except listen to the music. Which does not help productivity, as you might imagine.
Still, music helps shape what I'm writing, or rather, when I'm listening to music while something's in process, songs will jump out at me and I'll think, "This reminds me of a scene...." Or maybe a character or an overall feeling for the story or book.
For The Unwanted, I think the first song that jumped out at me came during a run (which I also sometimes make playlists for). I tend to listen to a lot of electronic music when I run; BT and Tiësto are in frequent rotation. When "Heroes," from Tiësto's album Parade of the Athletes came up on shuffle, it reminded me of three of my characters in a moment right before a particular scene. After I finished my run, I came home and started a playlist.
In case you're interested, I've put it up on Spotify—it's embedded below, but if that doesn't work for you, here's a link. Not all of the songs I listened to are available in their database; two tracks also on the list are "Bryan Sometimes" by Venus Hum and the audio track from the climax of the "Doomsday" episode of Doctor Who. You know the scene.