The Tenchi Muyo Fanfiction Archive (TMFFA):  Where most of the best Tenchi Muyo fanfiction can be found.  Umaro and I are both published there as well as on this site.  Definitely check it out.

Fanfiction.net:  An insanely large site with fanfics for nearly every show, book, and movie in existence...and then some.

Jenfic.com:  A great site which contains not only a variety of fanfiction, but also fan art, an image gallery, winamp skins and more!

The Shoujo Ai Archive: A very well-made site devoted to shoujo ai. They have fanfiction, a forum, a chat room, and other very cool features. I myself am a registered member there. Please go in there with an open mind, and PLEASE do not go in there with a disrespectful hentai freak mentality.