The kind of thing I'm writing or doing will influence the type of music. If I'm strategizing, something without words is better--Jazz or classical. If I'm editing, I have a certain couple of CDs with piano music that are a must--again without words. If I'm composing and letting the words flow, the music has to be current. I'm particularly fond of alternative rock, but anything that masks the brain noise seems to unleash the words.
The music helps keep me from getting stuck. The lyrics don't distract me. If fact, I hardly even register them until I start getting hung up and things stop flowing. Then I just lean back in my chair and listen, and the pounding rhythm, the complexities of the melody, the soaring or hushed or raspy vocals all help unwind my tangled thoughts. Then I can move on and keep writing.