There are a lot of good FY sites out there; some of the best are listed here, by category. I've also found images/sounds/songs/videos from these sites. If you think you've got a stupendous site that belongs on this list, E-mail Kazangana Masako (that's me!).

General - FY site listings, fansub distributors, and comprehensive sites	Anipike's Fushigi Yuugi Listings - If you just want listings of a LOT of sites! Tasuki no Miko's FY Page - Tasuki shrine, manga translations, info on the seiyuu (voice actors), image gallery, lyrics to songs . . . a very cool site.
Information - Good character and/or plot summaries	Adventure in the Universe of the Four Gods - by EX Magazine. General information. Reika-chan's FY Page - Manga translations, character pages, and episode summaries. Tomo no Miko's FY Page - Character info, seiyuu info, Tomo info (eagh!), image gallery . . .
Media - Has good sounds, pics, songs, or videos	Kiki's Fushigi Yuugi Image Gallery - Lots of images from the art books