Burke Rukes website features an extensive collection of Gundam and non-Gundam mecha specs, together with linearts and pictures. In the "Burke's All the World's Mobile Weapons" you'll find the background of every mecha.
Gundam Project [ http://www.gundamproject.com ]
What you'll find here are extensive descriptions and data about every Gundam serie you can think of, with story synopsis, cast and credit informations plus mecha related notes and arts by Mark Simmons.
Gundam.Com [ http://www.gundam.com ]
This site by Ben "Amuro Rei" Koshy is a real community center. It has the usual serie and mecha informations, but also features a large database of fan-art and fan modelkits.
Church of the Machine [ http://come.to/the_church ]
If you arelooking for extremely well built Gundam modelkits, look no further than Joc Tejapaibul's website. Not only the models are good, but the pictures in the galleries are crisp clear, completed with making notes.
Q.C.'s Anime Studio [ http://www.geocities.com/temjin_chen ]
Qi Feng Chen is a very talented artist, and on his site you'll find a gallery of interesting pictures, both hand-drawn and computer generated. Some of them have Gundam as their subject.
The Jeeg Page [ http://www.geocities.com/thejeeg ]
This is a site for the robot fan, boasting computer generated images of many new and old anime robots, from Mazinga-Z to the Guntank. Have a look at Gianni Soldati art galleries.
RX Homepage [ http://www.geocities.com/RX_79_V ]
RX's site features his own artworks, from pencil and paper sketches to CG works. It has a good picture gallery (all pictures made by RX, the original robots are excellent) and an interesting links section.
Newtype Asylum [ http://side7.gundam.com/newtype_asylum ]
At Newtype Asylum I found a lot of Gundam model reviews, informations on Gundam mecha and characters and a gallery of pictures taken from various Gundam series. Nightingale NT and Core are the guys behind this higly informative website.
Gianluca Panebianco Home of 3D[ http://www.panebianco3d.com ]
Gianluca Panebianco is a skilled CGI artist who created a comprehensive serie of 3D robot models from different anime shows. His site features image galleries, modeling tips and informations about the robots.