Found this one via Smart Bitches as well. I don't like the song "Somebody That I Used to Know" by Gotye all that much (it's okay, but it's really overplayed). But this a capella group, Pentatonix, gives it a whole new sound and brings new life to it. They sound amazing. There are places where it sounds like they must have musical accompaniment. But I think it's actually all a capella.