The first real Spike/Xander story I read was Esmeralda's Stranger Things (http://dea.certes.tripod.com/strangerthings/index.htm) series. Spike rescues Xander from a tribe of demons by convincing them Xander is his. They evolve into a relationship, then they get Angel involved, the Doyle (who is not dead). Very long, lots of smut. It's not quite what I look for in a fic now, but I still enjoy it, and it completely blew me away at the time.

I know you're totally familiar with amejisuto's Hold Me. Thrill Me. Kiss Me. Kill Me. (http://www.ameswierdness.com/viewstory.php?sid=60&ageconsent=ok) Xander meets Spike the summer before junior year. This one is still awesome.

You may feel odd about self-reccing, but Teenage Dirtbag and Grief Counseling are way up on my list of Spike/Xander recs, always.

Everything that reremouse has ever written, but especially Scoffs at Gravity (http://www.livejournal.com/tools/memories.bml?user=reremouse&keyword=Scoffs+At+Gravity&filter=all). Xander goes to liaise with Wolfram & Hart post-Chosen.

Kay's Spander in Spandex (http://www.athenewolfe.com/justrewards/viewstory.php?sid=1175). The title worried me, but it's so much fun. The Scoobies and Fang Gang on the Tour de France. What's not to love?

Everything savoytruffle has ever written, but I'm going to specifically mention Dirty Dancing Spander Style (http://www.livejournal.com/tools/memories.bml?user=savoytruffle&keyword=My+fic:+Dirty+Dancing+Spander+Style&filter=all), because I never would have thought this fusion could work and it so, so did.

Reconstruction, Restoration, and Reunification (http://www.angelfire.com/darkside/wordsmith/wordsmith.html) by Wordsmith are still stories close to my heart. I adore Xander-taking-charge fics.

And speaking of post-Grave fics, crazydiamondsue's Sunday Morning Coming Down (http://www.angelfire.com/fang/journals/arvs/crazydiamondsue/sundaymorning.html) is fantabulous. Much as I love Xander in control, Xander falling apart in the wake of Buffy's death can be pretty amazing, too.

I'm sure I'll think of more, but I don't want to spam you too much. :o)