There is really not a lot in terms of Azumanga Daioh sites out there. Here's a small list of Azu-related stuff. If you would like your site added to this list, please email me and I'll be happy to do so. I will only add Azumanga sites though.

English:
A!
ADV's Official Azumanga site
Azumanga Daioh Images
Azumanga Daioh Web
Great King Shezotaku's Episode Guide
Happy: A dedication to Chiyo and Osaka
Obtuse
Raspberry Heaven
Sata Andagi!

French:
Azumanga Daioh
Azumanga Daioh

Japanese:
Azumanga-TV-Daioh
TV Tokyo

Fanlistings:
Azumanga Daioh
Chiyo
Kamineko
Sakaki
Osaka

Reviews:
Anime Academy
Animefringe
Freetype
Furinkan.net
Pulp Film

Link Me: