It's astonishing just how many instruments are out there--and new ones being invented all the time. If you're doing a bit of world-building, it's definitely worth thinking about what the music would sound like, because it probably wouldn't be what's on the top-40 stations around here, or even what's being played at most orchestral concerts. Here's a range of things from silly to cool to profound:
Posts from This Journal by “youtube” Tag
Or quite a few. :D
A fascinating little time-capsule of a (fan-made) music video.