I've made something for my desk at work.
I bought a reindeer made from twigs and some battery powered lights that spell out 'happy Christmas'.
I programmed my adruino to play Christmas tunes (available in another thread) and flash the lights when you press a button. I then put the arduino in a box and wrapped it up like a present. It takes its power from USB so I can plug it in to my PC at work.
Here's a low quality video of it:
I did have an LED display showing "n DAYS UNTIL CHRISTMAS!" but I guess I ran out of memory cos I couldn't get it and the tunes working at the same time.
CowJam