Without a shadow of a doubt the best xmas movie is Santa Claus: The Movie, with Dudley Moore as the main elf. It's fantastic. It isn't christmas without this movie. I watch it every year without fail on Christmas Eve, and have done since I was a little kid.
I also like the Muppets Christmas Carol. And of course the first couple of Home Alone films. Not keen on the other Home Alone's - it's just not as good without Macaulay Culkin.
I like watching films that are set in winter or at christmas time, like While You Were Sleeping with Sandra Bullock. Narnia is good too as it's all snowy.
Yay, i can't wait for Christmas now - i love it. It's great when it's winter and you get all snuggly with big baggy jumpers and blankets, and drink hot chocolate out of a big mug......woo hoo!