Christmas 2 years ago I heard a choir in London sing this acapella in the street and was stopped in my tracks, amazed how a dozen people could make such an incredible sound - one of those moments where you hear something and emotion comes from nowhere (I'm a sucker for vocal harmonies in any music too). Have listened to it 3,536,312 (approx) times since at a guess. There's loads of versions online but this is the one I found on the train home that night and bookmarked.