Ideas company AKQA has created one of the coolest Christmas video cards I've ever seen: 49 microwave ovens stacked on a wall, all set to play Jingle Bells.
As you can see in the video, it required some careful planning. First, finding the microwave ovens with the right "ping", so they could have the notes required to play Jingle Bells. Then, setting up the timers so, when the cooking time was done, the pings created the song. It can't beat that Burt & Loni Sing Xmas vinyl. but it's absolute genius.