Hitoshi Doi Seiyuu Database - For when you need to know who played who.
Godchecker - An excellent resource of information on gods from numerous cultures.
Go Definitions - Plenty of terminology useful for authors of Hikaru no Go fics
Fanfic Symposium - A variety of essays about various aspects of fanfic writing. Though its primary focus is on North American media fandoms, there's plenty here relevant to anime writers as well.
Staykas' Saint Seiya Archive - The one-stop resource for all things Saint Seiya. Image galleries, a huge link archive and more.
Good Vibrations - The "Good Vibes Magazine" section of this well-known sexual products site has plenty of good, solid information on numerous aspects of sexuality. An excellent resource for lemon writers. For yaoi writers, the "Ten Rules of Anal Sex" article, found under the "Info Desk" heading and "Sexual Health/Product Info" subheading of the site, is an absolute must-read. Must be 21 to enter.
Dreams of Sakura - Informational page about X, also features Alison Koh's excellent fanfics (mostly SubaruXKamui) and the Sakura Board BBS.
Jumpy Boys! - Fanfiction archive focused on anime and manga that had its beginning in the pages of Shonen Jump.
Go-Luv v2.0 -- HikaGoYaoi.org - Web site for the Hikaru no Go fan community. Its bulletin board section includes information, fanart and fanfiction. The site also has some translated doujinshi.
Mediaminer.org - General anime fanfic site, accepts fics of all ratings.
Hitoshi Doi Sailor Moon Encyclopedia - Information on characters, storyline and merchandise.
Theria's Yami no Matsuei Page - With information on both anime and manga, plus manga translations.
Aya no Weiss Kreuz Corner - Has a comprehensive discography including some lyric translations, translations of some of the drama CDs, and more information.