Not really all-KND but some KND-related questions are asked on the Ask Mo section.
FanFiction.net, Codename: Kids Next Door
KND fanfics!
Numbuh 8-bit star's KND page
Very detailed BIOs and episode descriptions and great articals!
Operation: Fansite
Very cool site with a great KND froum.
Bizarro's Domain
The site with the best Fanart, nuff said.
Abby's KND and All Grown Up Site
Cute KND and AGU fansite ^^.
Codename: Kids Next Door in Operation: H.A.L.O.
Another cool KND fansite.
KartoonsRKewl
Wow, I can't belive I haven't linked this site earlier, Anyway a cute KND and MLAATR fansite.
Numbuh 666's KND fansite
Great in-depth character profiles.
Kewl KND site
And a kewl KND site it is ^_~ Great job Numbuh 14.
Kawaii No Desu!
I love this site, it has really great fanart and a HUGE Romance section.
.:Character Profiles:.
.:Episode summerys:.
.:Romance:.
.:M.Y.O. Character:.
.:Fan Art:.
.:Fan Fiction:.
.:About me:.
.:Links:.