Bing Crosby's "White Christmas", one of the best ever. I really like Mannheim Steamroller's version of just about every Christmas song, but "Carol of the Bells" is particularly neat. I guess the people who used it for their light display thought so, too!
[ame=http://www.youtube.com/watch?v=uuJSJAi9ZpM]Christmas Lights - Carol of the Bells - YouTube[/ame]