OH! I know this one. It's "Better to Give than Receive" by ImmortallySpuffy.
Buffy does in fact receive Christmas gifts that are related to the word 'spike'.
http://dark-solace.org/elysian/viewstory.php?sid=1491Summary: In response to the FangFetish Holiday Challenge. Buffy get Christmas gifts from her mortal enemy. She finds herself keeping them despite her feelings for Spike... and what's with the poetry? Different chapters were written by the following authors, MaryPerk, JackofSpikes and Kargrif. Banners by Kargrif.