Don't know if this has ever come up, but among the interpolations in scores that I love, Christmas songs is pretty high up. Some of my favorites:"No Santa Claus" (Silent Night) - Gremlins (maybe it's just me, but I found this scene - why Kate doesn't like Christmas - genuinely sad and Goldsmith's adaptation is a strong part of that)
"Christmas Eve Montage" (Jingle Bells) - Nightmare Before Christmas (toward the end of the cue, Elfman slipped this in, a nice counterpoint)
"Chased by Santa" (Deck the Halls) - the "Futurama" episode, "Xmas Story" (Chris Tyng's music for the show is great, and this is one of my favorites; not too many composers turn a carol into an action melody)
"Revenge of the Bladers" (12 Days of Christmas) - Mixed Nuts (another, all-too-rare action take on a carol)
"Gracie's a Hero...and a Mother" (12 Days, Good King Wenceslas, Jingle Bells, Joy to the World) - Mixed Nuts (this film had some good music, but George Fenton must've really been inspired by that last reel or so)
"Christmas Shopping" (Carol of the Bells) - Turbulence (I've never been too big on this melody, but Shirley Walker imbued it with a terrific sense of unease)
And what about Christmas standards?
"Alaska" (Winter Wonderland) - North (about halfway into Shaiman's track, past the glitzy take on the song, there's a melancholy read of it that is beautiful)
"Smuntzes Lament" (I'll Be Home for Christmas) - Mouse Hunt (I just love this heartwarming version of it, another great touch in this underrated Silvestri effort)
Any other favorites?
Right before they shoot that old lady up the stairs and out the window, to her deservedly terrifying death. GO GREMLINS