Wish is one of CLAMP's definitely less popular series; and it's rather difficult to find quality sites , actually any site dedicated to it. I'll list those which I find to be well set-up and overall interesting to visit:
Your Eden... - http://sakurazukamori.net/eden
My sister Val's wonderful "Your Eden..." is a definite must-visit for anybody who is interested in deep character analysis and other great content. Go there, now ! ^^
Usyagi's Wish Site - http://come.to/mywish
To be quite honest, I am not too sure whether Usyagi's Site is still being updated... but nevertheless, it offers good overall information on the series, with original things such as a description of the gemstones featured in the series and other nice things.
X-Playboy - http://cherry-blossom.nu/kokuyo/
A small but promising shrine to my second favorite character; Kokyou. It's nice to see a dedication to him out there ^^
Black & White - http://megitsune.net/kokuyou/
Oh, people say Kouryuu's the popular bishounen in WISH, but actually Kokyou seems to be the one that is getting more & more shrines! ^_~
At any rate, this shrine is nicely done with a *very* good, analytical character description.