When my wife and I were dating, we watched White Christmas on TV together. Though we had seen it separately many times, it really clicked with us that night. It has since become a Christmas Eve tradition (by the way, the White Christmas DVD features glorious color and comes highly recommended). Christmas Eve just wouldn't be the same without watching White Christmas...though, honestly, if we couldn't see it for some reason, I think we could almost reenact it scene for scene.
We also try to squeeze in The Bishop's Wife and Chrsitmas in Connecticut each December. That old reliable favorite, It's a Wonderful Life, has been been overexposed. But I still remember the emotional impact of my first viewing and if I'm channel-surfing when it's on, I often end up watching the rest of the movie.
Sometimes, a movie with no holiday connections, can become a seasonal tradition. For many years, my wife and I watched The Ghost and Mrs. Muir on New Year's Eve. There's nothing about New Year in the movie, but there is a magical, timeless quality which somehow made it a perfect way to close out the old year.
So, what are your holiday movie or TV traditions?