Mine, without a doubt, is 'The Holiday.' Such a great movie and I've watched it every year to usher in the Christmas season for a long time. It means "Christmas is here" to me. I started my love affair with the movie when Riley and I were studying abroad in Italy, whenever we missed our families we would think about Christmas and seeing them, and started watching this movie in approximately October. I think we watched it about 15 times!
If you haven't seen it, go rent it RIGHT NOW!