This may come as a shock to a lot of people, but almost everything that I write pertaining to the Buffyverse is one way or another about Spike and Buffy. They may be friends, they may, be lovers, they may be mortal enemies, but it always, for some reason or other, gets down to them.
Beyond that, I have written a couple of Buffy/Faith "buddy" stories, one Bangel story (romantic and sad, basically a rip off of "Casablanca") during my "made a promise to a lady" month, and, just as an experiment once, I tried (VERY unsuccessfully) to write a mildly erotic story concerning Angel, Faith, Buffy, and Spike (poor Angel will never be the same again)
I also did, right after "Not Fade Away" aired for the first time, a Buffy/Angel/Highlander/Alamo (yes, THAT Alamo) crossover that was a lot of fun doing, but will never see the light of day again. I'll give you this much of an explanation on that one: Willow raised a fallen army of heroes to help bail Angel and his crew out in the final battle. Beyond that, my lips are forever sealed.