I've been listening to various versions of "Hallelujah" lately thanks in large part to Malcolm Gladwell's Revisionist History episode on the song (I wrote about that here). It's a great song and it's always cool to see different artists cover it in their own way (in fact, arguably the most popular version of the song is a cover of the original!).
Anyway, here's Pentatonix doing a great acapella version of the song.