I just “Christmased Up” my iMac here at work and thought I’d share the links of the stuff I found (all free).
First, there’s the awesome OpenGL Snowfall screensaver. It’s very customizable (different or no background colors, images, etc).
Next, X-masTree (direct download link). This puts a nice (and also very customizable) Christmas Tree on your desktop. It can even include a countdown badge for the days until Christmas. It’s so customizable, it even works for people who celebrate Christmas on January 7! Who the heck celebrates Christmas on January 7?!
Third is MacLampsX. This one was too gaudy for my tastes, but fun to play around with for a couple minutes. If it suits you, I won’t judge.
Lastly, I searched Google Images for a few wintry snowscape pictures. This one was my favorite and I set it to my Desktop background (until I get bored with it and decide to change it). We have a picture of that famous bridge from when we were there (but it was summer then).