Many people righteously argue that Die Hard is the best Christmas movie ever, or that Love Actually is more than the sum of its parts, or that it isn't Christmas without It's A Wonderful Life. But as far as I'm concerned, the ultimate Christmas movie will always be Where Eagles Dare.
It was on several times on Christmas Day, seen as good, clean fun as Clint Eastwood, Richard Burton and Mary Ure murder a whole bunch of people. It's okay, because they're all Nazis, and fuck those guys.
Me and my Dad would watch it every year it was on, and he usually fell asleep for the long scene around the tablle where they're double crossing the hell out of each other, but always woke up again when the murdering began in earnest. It's snowy and has a great theme tune and lots and lots of Nazis get blown to hell. It's everything you could want in a Christmas movie.