I agree that consideration of other riders is key, and there are times when silence is golden. That having been said, I find that just about anything by Green Day helps me power through a training ride. For the tandem, my stoker is partial to Springsteen, Bob Dylan, Neil Young, etc. Atmosphere music. That's the beauty of Pandora - you can seed it with a song or artist, and it plays music of the same style, tempo, etc. Good variety without having to surf the same list of static mp3's on your handheld.