Very good page concerning RED MARS and K.S.Robinson:
http://hubcap.clemson.edu/~sparks/marsindx.html

One of the best sites on K.S. Robinson's Mars trilogy:
http://www.xs4all.nl/~fwb/rgbmars.html

Another unofficial site featuring the Mars trilogy:
http://mars.deltos.com

If you are interested in what PATHFINDER did on Mars go here:
http://mars.sgi.com/default.html

A nice German site with information about Mars, ISS a.m.m.:
http://members.myworld.at/nosig/

NASA's official site:
http://www.nasa.gov

Website of the German Chapter of the Mars Society:
http://www.marssociety.de

Website of the International Mars Society:
http://www.marssociety.com