Below are my must-sees: the films that matter to me for one reason or the other. None is terribly unique (except maybe It's Only Money), but that's only on the list because it shows a California Christmas -- and nothing in 1951 could have been odder than a film in which there are Christmas trees among the palms.
1) Miracle on 34th Street (1947): Maureen O'Hara, Edmund Gwenn, John Payne, and Natalie Wood http://www.youtube.com/watch?v=0IZr_SvCcXc
The gold standard of Christmas movies. Brilliantly written and acted. A nice balance between fantasy and reality (personal, corporate, and political). And a young Natalie Wood who shows already why she'd grow up into "Natalie Wood."
2) It's Only Money, a.k.a. Double Dynamite (1951): Frank Sinatra, Groucho Marx, Jane Russell http://www.guba.com/watch/3000092384
Jane Russell can't act or sing, but, as released in 1951 by boyfriend Howard Hughes, she gets the title role since she's packing the "Double Dynamite" in her sweater! Happy Holidays, gentlemen.
3) The Little Drummer Boy (1968): Jose Ferrer, Greer Garson
Greer Garson, with whom I first fell in love when I saw Mrs. Miniver, narrates this Rankin/Bass take on the nativity story and familiar Christmas song. Jose Ferrer as the "desert showman" is pretty swell too. And it's always nice to see at least a cameo by Jesus in a Christmas film.
4) A Christmas Story (1983): Darren McGavin, Melinda Dillon, Peter Billingsley http://www.youtube.com/watch?v=3mjruvE310Y
Nostalgic and funny. VERY funny.