Here's a link to Paste Magazine's recommendations for holiday beers, and it's a pretty good list. Obviously I haven't sampled all of these, but any list that has as product from the Left Hand Brewing Company is heading in the right direction; all of their beers are superlative, and in particular I'd recommend their Saw Tooth Ale and Milk Stout. Anchor, Sierra Nevada, and Rogue are also beers onthe list that I can vouch for, in terms of their Holiday Cheer!
I would add to the list Saranac's Season's Best, and Big Sky's Powder Hound Winter Ale. Friends of mine chipped in with Sam Adam's Winter, Harpoon Winter Warmer, and Magic Hat Roxy Rolles. As I'm always on the lookout for interesting beers to try, including seasonals, please list any not mentioned above. I should also note that the "Postcards from the Id" Vallina Porter was brewed this December, and sampled for the first time last night to solid results. Probably the second most difficult beer I've tried to make (first being a barley wine), so I'm very pleased with the results.
Hope everyone is having a great Holiday season. Merry Christmas!