I have to say that, in all honesty, this is the most amazing Yu Yu Hakusho site I've ever seen. It is to Yu Yu Hakusho what Priya and Kristi's Shrine to the Almighty Chicken of Doom is to Fushigi Yuugi. This site has a plot summary of the entire series, character descriptions of everyone you can think of, pictures, audio files, song lyrics, a voting pole, CD and seiyuu information, extensive fan art, links to some great sites, and a lot more. I highly recommend it.
The one and only (as far as I know) shrine to the most deserving Lord of the Makai, Yomi-sama, with information, pictures, fanfiction and fanart - in English or Portuguese.
Sites for information, pictures, links and music
Yu Yu Hakusho!
The Ultimate Yuu* Yuu* Hakusho
[Yu Yu Hakusho]
Sites for fanfiction
Yu*Yu*Hakusho Fan Fiction Archive
Yu Yu Hakusho Fanfictions
Hiei and Kurama's Den
Julie's Anime Home Page
The Universe of the Fox and the Phoenix
Utopian Trunks' Fanfiction
Youko Kurama's Yu Yu Hakusho Fanfiction
Shiromori's Kyuuketsuki Miyu Page
Kitsune's Fushigi no Peiji