Jubilee by Idle Time Software displays Christmas or Hannukah lights like you'd see them if you were rocketing through your neighborhood in a Ferrari. There are four color schemes, including a beautiful blue and white Hanukkah theme. It requires Mac OS X 10.4 + (including Snow Leopard) and the Flash plugin.
XMas Tree by Joe Hillman is an interesting 3D screen saver that decorates your desktop with textured ornaments. It's strangely hypnotic as the screen rotates around a beautifully generated 3D tree while Christmas music plays in the background. Mac OS X 10.5 + (including Snow Leopard).
Silver Snow Clock is a simple little saver that shows an ornate pocket watch ticking the time away as the holidays pass us by. This gets a mention as one of my favorites because of the 3D snow that gently drizzles down the screen. Mac OS X 10.5 + (including Snow Leopard).
Last but not least is everyone's favorite, Snowfall by Russel Warnebolt. We first reported on this almost three years ago, but it still deserves top marks.
Contrary to popular belief, this screen saver was never used in Apple's retail stores (that one was, sadly, Apple-internal only). Since updating to 10.6.2, Snowfall experiences slight jitters. According to the dev: 'This appears to be a newly introduced bug in Quartz Composer on 10.6.2 that causes very poor frame rate. On 10.6 and 10.6.1 things are as usual, at least on my machines. Unfortunately this may require a fix from Apple.' Nonetheless, it's still the most beautiful Christmas screen saver I've ever seen. Mac OS X 10.4 + (including Snow Leopard).