I've only recently found Peasant's Buffy fic. I haven't had time to read anything except Sweet William -- but let me protest that this is an actual novel, and a heavy-duty one at that. Spike's first few years as a vampire, with Angelus as his guide. I've seen the mentor/fledgling dynamic done lots of ways in fic, but rarely have I been so fascinated by every single line, so invested in every action and reaction.
Bonus: while you're at this site, check out History of the Aurelian Vampires.
Bonus: while you're at this site, check out History of the Aurelian Vampires.