I read some Yuletide fics this year and found several I wanted to mention. The fandoms are wildly disparate, so I'll just list them in alphabetical order.
Aliens vs. Predators - "
La Luna del Cacciatore". The movie isn't all that great, but there are some things about it I like a lot, and this fic takes those things and makes an intriguing alternate ending.
Downton Abbey - "
In Translation". Mary/Matthew. Set after the season finale. I like the format used here and the writing is sad and lovely.
Greek Mythology - "
Gorgoneia". About the gorgons, what they once were and what happened to the two remaining ones, Stheno and Euryale, through the centuries. Simply haunting.
Haven - "
Sand Castles". Audrey/Duke. M-rated. Spoilers for the season finale. I'm quite fond of Nathan, but these two really need to get together, and this is wonderful.
Terminator: The Sarah Connor Chronicles - "
To Learn the Games You Play". Spoilers for the series. Allison of Palmdale, who never did stand a chance. This captures her desperation painfully well.