Koenma and Botan - Fics in a Nutshell - excellent site for Koenma and Botan ficcies. Koenma goodies...always a good thing.
The Ghost Guild - Yu Yu Hakusho 'webring' of sorts where I'm a new member. Check out the other sites!
Milk and Honey - mini-shrine to Koenma, by Tenshi no Korin. Beware of yaoi, but delight in the awesome pictures and the fact that it *is* a shrine to Koenma
Koenma, Little Lord of the Underworld - cute Koenma shrine
Shall We Dance? - must see couple shrine
Candy Pop - Japanese Koenma & Botan site (I think...at least that's what it looked like)
The Reikai Couple - Koenma + Botan - self-explanatory. Extremely cool K + B shrine.
Traversing Hearts - not a Koenma site, but a Yu Yu Hakusho/Inuyasha crossover fan site. *ahem* Note the first story on the fanfic page.
Aaron's Tools - *awesome* site graphics. In Japanese or English.