FanFiction.Net: Gundam UC: Collection of U.C.-based Gundam fan fiction, with search engine, list of authors / columnists, reviews and fan forum.
Gundam Fan Fiction Archive (from The Eyrie): Archive of Gundam and anime-related on-line fan fiction.
Gundam Zach: Original UC-based story, plus other fan fictions and comics.
Newtype Alpha Productions: Collection of Universal Century Gundam fan fiction. Fan's submissions are welcome.