The music I listen to depends on what I'm writing. When writing fiction, I listen to music that puts me in a particular mood, whether happy and inspired or sad and lonely. I want to feel the same way as the characters in the scene. Usually classical and R&B work well for this.
If I need to write very fast in a short time, I listen to something more intense like hip-hop, pop, and occasionally rock. I don't pay attention to the lyrics, I just let the music accompany my writing.
When concentration is required, I need complete silence.