4» Center of the Universe: Fan Fic Archive
"Center of the Universe" recently changed hands and is no longer accessible. Hopefully, it will be back up soon. It was a great place to find various fanfics, especially Sailor Moon ones, and it should be again when it comes back.
4» Castle of the Invented Senshi
While this is technically not a "fanfiction" links, it involves fan work of Sailor Moon, much of which is bound to be fanfiction. "Castle of the Invented Senshi" is an amalgam of a "gallery" site, where certain pages represent "rooms," and a directory. This is the best place to go if you're looking to see the different versions of invented Sailor Moon characters out there, especially the more popular ones such as Sailor Sun and Sailor Earth.
2» The Definitive Sailor Moon Fanfic Directory
Yep, it's pretty definitive. If you're looking to read any Sailor Moon fanfiction, this is the place to start from. Not only does it serve as a directory itself, it also has a listing of other popular Sailor Moon fanfiction directories online. If this site should happen to fail you, there's always Google.
3» Usagi: Sailor Neomoon
Finally. A fanfiction saga without the "a mysterious new senshi appears!" premise. And, finally, they stopped calling her "Chibi-Usa"! All grown up, the pink-haired girl now goes by "Usagi" and becomes the hero of a new generation.