Constructing an SF Universe Excellent article by professional, published science fiction author, S. Andrew Swann. http://www.sff.net/people/SASwann/text/wb.htm

Pegasus Nest: Worldbuilding The page is oriented toward fantasy/science fiction writers, BUT the principles of good worldbuilding should apply to rpg's as well. http://yhl.freeservers.com/yhlwork/advice.html

Planetary Fact Sheets Extensive physical data describing the planets, satellites, and comets of our solar system, courtesy of NASA's National Space Science Data Center. Potentially useful to designers of science fiction settings and the detail-minded. http://nssdc.gsfc.nasa.gov/planetary/planetfact.html

One Man's Views of 2300AD Features new adventures, art, campaign background, characters, equipment, monsters, vehicles, weapons, plus product reviews and links. http://home.earthlink.net/~ad2300/