The Shrine of Gamera: The best Gamera site that I’ve ever seen.  It contains summaries of all of the Gamera films plus previews for Gamera III.

The official Gamera III site on the net (English version).  Contains news about Gamera III and much more.  

The ADV Films Gamera page:  This is pretty sweet Gamera page.  If you’re looking for pics, movies, and anything else you’ll probably find it here.