It's a good thing we just got finished with an apocafic, because this year we're going to have two fics for Christmas and they're both sweet and generally happy little stories. Everyone is welcome to comment on both, or only one, in either order, at any time.
The first one is an AU season 9-ish fic in which Mulder and Scully spend Christmas together with their infant son. It's also probably the most homey, domestic fic I'm ever going to rec. *g* But don't let my Scrooge impression scare you off. It's nice, and there's an interesting little twist to Mulder and Scully's world, amidst all the domestic bliss.
Epiphany by Maybe Amanda
In the second fic, Mulder and Scully spend Christmas Eve stranded while on the road. It's set in any one of the early/mid seasons, and it's nothing complicated, just a sweetly romantic little vignette.
How to Fly by Oracle
Merry Christmas to all who celebrate, and seasonal well wishes to all who don't.