Here goes nothing:
Buffy The Vampire Slayer
Dang Me (PG-15, Language)
One-Shot: Spike and Xander get drunk while the power's out. Spike learns the Legend of Droopy Harris.
Treading Water (PG-15, Language, mentions of Xander/Jesse, and Xander/Bad!Guy before the Spander)
Four chapters: Xander accidentally summons a "genie". And learns that grief can't be soothed by magical means.
Apart (R, Language, Sexual Content, mentions of Alcoholism)
Four chapters: Annoyed with their constant bickering, Willow spells Spike and Xander apart. But it turns out the boys really do need each other.
Evil Things (PG-13/Light R, Language, Dark!Xander)
One-Shot: Xander has dug a hole. Now it's time to fill it up.
Orbit (NC-17, Language, Recreational Drug Use, Sexual Content)
One-Shot: Spike witnesses Xander getting high and screwing around with an idiot named Steve in the alley behind the Bronze. He joins them.
Paper: Follow-Up To Orbit (NC-17, Language, Sexual Content, Recreational Drug Use)
One-Shot: Spike reconnects with his inner poet as he and Xander get stoned together.
The Three Dog Nights Series (NC-17, Explicit Sexual Content, Language):
Never Been To Spain | Let Me Serenade You | Shambala
Three parts, in a total of eight sections: Spike catches Xander reading a book on how to seduce demons, and offers to... "tutor" him on the subject. This is just wonderful, since the demon Xander had been hoping to seduce was Spike.
It's Been A While (R, Language, Phonesex, Brief Allusions To: Spike/Angel, Xander/OMC, Spike/OMC)
Three Chapters: Xander and Spike reconnect over the phone. And realize some things.
Romance Is Dead (NC-17, Cowrite with amyww, Smut, Violence)
An old friend of Xander's shows up to interrupt his and Spike's Halloween night. In the process, Spike... learns a few things about Xander.
Doin' The Pouncing (Light R, Language, Implied Sex)
Spike seduces Xander over the course of three breakfasts.
My Cruddy Valentine (Light R, Language, Implied Xander/Bad!Guy)
Valentine's Day Fic! Xander has been experimenting with guys... Of course, he's Xander, so he winds up experimenting with the wrong person. Total cliche fluff.
That Comment!Fic With Witchway (NC-17, Explicit Sexual Content)
Part One | Part Two
Rizzoli & Isles
Fluff (NC-17, Explicit Sexual Content)
Both figurative, and literal.