This is probably my favorite Christmas song/melody. Instrumental or sung, electric guitar or organ or even bells, I have rarely found a version that I didn't like. Admittedly, it's a touch ironic to have the Carol of the Bells done a capella. For the non-musically-literate, that means "voices only; no instruments." And this version is awesome.
(Found via this link from James McGrath)
AM UPDATE: Fixed broken link (somehow two links got interpolated, so blogger decided to just make it link back to my blog). Oh, and I thought of one version of Carol of the Bells that I didn't care for. Showed up in a holiday commercial, which may or may not still be used this season. I can't even remember what it was an ad for... possibly one of those navigation devices for the car. But it was just irritating.