The Eureka Seven Unofficial Forum at http://z7.invisionfree.com/Eureka_Seven has been online discussing Eureka Seven since June 4, 2006. It currently has 3,828 members and 169,136 posts (as of March 11, 2010 at 4:52 p.m. CST).
The forum was started by a user called Matt122004.
One of its success stories regarding Eureka Seven was it broke the news of a movie (Eureka Seven: Pocketful of Rainbows) being made before many mainstream news organizations had the information (i.e., AnimeNewsNetwork.com).
The forum also features interviews with english voice actors from the series and with Dai Sato (scriptwriter and series composition for Eureka Seven).
Topics of discussion include all aspects of Eureka Seven, other animes and off topic.