In League With Serpents by weyrwolfen
Summary: When Spike wins something unexpected over a game of cards, he ends up with a most unlikely crypt-mate and a mission to help a newly resurrected Buffy. With an empathic serpent setting up shop in his head, a scheming warlock on his tail, and a bothersome change in his relationship with the Scoobies, Spike finds himself in the position to save the slayer he loves, the world, and maybe himself in the offing.
http://spikeluver.com/SpuffyRealm/viewstory.php?sid=15577and it's sequel
Feathers and Forked Tongues has a great Dawn/Spike and Tara/Spike friendship.
http://spikeluver.com/SpuffyRealm/viewstory.php?sid=18720These are two of my favorite fics.