Kismet
This story starts with a flashback to Spike's life as a child, moves to what looks like a simple B/S hurt/comfort story, and ends up somwhere completely unexpected. Kismet keeps the action going and the angst flowing in this completely gripping (and entirely plausible) story. I was enthralled from the first sentence straight through to the end.
I think what I like best about Kismet's writing is how she is able to juggle several points of view without having all her characters sound like each other, and keeping them in line with what we know of them. There are rules to writing good fanfiction, and she is able to adhere to them and still tell her story, her way.