I can only play instrumental pieces while I'm writing. Anything with lyrics becomes really distracting, and I find my output dropping to almost nothing. That being said, there's a LOT of great instrumental stuff I've used for inspiration, usually dependent on the genre. For example, Koh Ohtani's soundtrack to Shadow of the Colossus is one of the most beautiful orchestral works I know, and is perfect for putting me into a grand fantasy mindset. I also listened to a lot of instrumental Nine Inch Nails and Juno Reactor while writing Alpha Slip - I think the faster pace actually helped with keeping my writing style hard and clipped. I don't go so far as to find a sad song for a boohoo scene, but I have used slow songs to help me pace more lanquid scenes (BT's 'This Binary Universe' album is fantastic for that purpose).