First, a series of linked fics featuring Spike's ongoing feud with that notorious badass, Santa Claus.
The Night Before Christmas. Spike and Dawn. PG.
Spike vs Santa Claus: the Rematch. Spike and ensemble from AtS season 5. PG.
The Revenge of Santa Claus. Spike/Buffy and Illyria. PG.
Then, in a different vein: The Truce. A slashy Christmas tale featuring Spike/Angel and rather a lot of alcohol. NC17.
And last, but by no means least, the reappearance of that other notorious badass, Fairy!Spike, in The Christmas Tree Fairy. Mention of various pairings, including Fairy!Vampire!Spike/Fairy!Vampire!Angelu