Depends on what kind of fic you're looking for...
I have one AtS fic on my site:
Mistletoe, Spongebob and *Thud* - totally fluff / corny / cheese / humorous - but fun... *g*
Pointy Stakes - this is Mad Poetess' site - she mostly writes S/X and various other slash-y pairings, but she has some AtS stuff - check the story index...
BtVS Writer's Guild - this is probably one of the best places to locate fic indeces... grab a genre, a pairing, etc... they have a zone for it and it will lead you to other places on the net for even more fic...
That should get you started...