This has always been one of my very favorite songs.  It has been recorded by virtually ever popular artist, some offering great renditions, others not so great.  There isn't really much to say about this one, it is just a classic.  The next time you watch the movie "Home Alone", pay special attention to the choir that sings while "Kevin" is taking refuge in the church.  It is remarkably good.  Follow the link below to the Amazon page for the soundtrack and click next to O Holy Night for a great sample.  Awesome stuff.