There are many seasonal brews that come around each winter, and some specially made for Christmas, so I thought I'd recommend some of the better ones I've tried this year.
Belgium makes an astounding number of Christmas beers, mostly double or trippel ales that are wonderfully rich and warming. Bottleworks in Seattle have a great selection, and when I stopped by a few weeks ago, the had some 1-year old Corsendonk Christmas Ale. I tried it last night, and really enjoyed it! It's mellow, smooth, a little nutty and spicy and not too fizzy. It reminded me a little of the Rogue Hazelnut brown ale, so try that one too if you like the Corsendonk...
Some of the newer Belgian beers can be really fizzy, I think the aging makes a big difference... I tried an Orval a few days previous and it was disappointingly fizzy.
Speaking of Bottleworks, they have recently opened a Belgian-style bar/cafe in Fremont, called Brouwer's, and I'm dying to try it. Perhaps there will be some moules et frites in my Christmas long-weekend!
Being a Seattle-ite, I can't write about beer and leave out the great Northwest microbrews that come out this time of year. Favourites from past years are the Sierra Nevada Celebration Ale, Redhook Brewery Winter Hook Ale and the Bridgeport Ebenezer Ale. I've recently tried the Pyramid Brewery Snow Cap Ale, but this was too bitter and hoppy for my tastes, and not very fruity or rich, so it isn't high on my list of winter ales.
Update: 1/3/2006
A quick note on some other beers I've tried in the past week or so.
A Pacific NW one that's very yummy is the Widmer Snow Plow. Very smooth and malty, nice and warming. It's sort of like Guiness-lite. (Not as bitter and charred)
Another great Belgian beer (not seasonal, though) was a bottle of Kwak . Something about the name appeals to my juvenile sense of humour. (Which is still intact despite my great age...)