Oddzilla Productions: Anime Fanfiction
One-shots and series based on Ranma 1/2; stories from Evangelion, Samurai Shodown, Ah! Megami-Sama!, and Sailor Moon.

Oni Playground
Fiction inspired by Gundam Wing, Slayers, and Yu Yu Hakusho.

Opal's Black Moon Junkyard
Works and screenshots.

OrangeRoad Fanfiction Page
Neon Genesis Evangelion and Vampire Princess Miyu works.

Otaku Dedicated to Quality Anime Fanfiction
Fiction separated by series. Includes submission rules.

Oki Doki
Fiction for various anime series, including Weiß Kreuz, Gundam Wing, Revolutionary Girl Utena, and Dragon Ball Z.

Otaku Park
Archive with tutorials on the Meiji Revolution and HTML. Series include Digimon: Digital Monsters, The Hakkenden, Neon Genesis Evangelion, Rurouni Kenshin, Sailor Moon, and Weiß Kreuz.

Obvious Conclusions
Fan fiction including Digimon and a Sailormoon/Buffy the Vampire Slayer crossover.

Operation Expurgation
Short story by Mangamaniac and PetBahamut inspired by anime and Final Fantasy, featuring the adventures of Lieutenant Tranchant and Subordinate Nazim.