White Christmas, because it's always on telly and I can't resist watching it because I love Danny Kaye.
And Camelot. Not exactly a Christmas film, apart from the bit at the beginning when Vanessa Redgrave/Guinevere is driven through a snowy forest, all wrapped up in a gorgeous fur-trimmed cloak and looking beautiful, and Richard Harris/Arthur sings to her about all the magic of Camelot. It's a wonderful film and the most beautiful and tragic love story.