Usually I listen to compositions without any sort of lyrics. I know it sounds odd, but I'm just not a fan of singing for the most part. I usually just find random compositions on the internet to listen to and download/keep ones I like. There's a lot of good music at ocremix.org. Some of Unreal Tournament's music is excellent. I've also found some good tracker music, and MIDI files that sound amazing when rendered with fluidsynth. Also, it's not really music, strictly speaking, but binaural beats can be interesting to listen to. Binaural beats are very simple and can even be made with Audacity.