Onizuka Sensei reccomends you go to..
EX Online Magazine
Has reviews for GTO, Parasyte, Tanabata no Kuni and lots of interesting stuff..
GTO # Intro
A GTO website in Thai
official webpage of the GTO comic (jp)
GTO Anime @Studio Pierrot
(jp) they have also animated Fushigi Yuugi and Ninja Robots if you're familiar with them..
GTO Movie @ Fuji TV
also in (jp)..
official homepage (jp)
Other Non GTO Websites..
Lots Anime/Manga (even GTO)
Info on Urusei Yatsura and Rumiko Takahashi