The treaties governing outer space and the solar system.
The Nine Planets page, produced by SEDS.
Welcome to the Planets, by JPL.
NASA's NSSDC has lots of information.
Views of the Solar System
The galaxy page has pointers to several tours of the solar system, and all the planets too.
The US Geological Survey's set of Solar System images.
U of Wisconsin has a course on Resources from Space. It describes resources on the moon and planets that will eventually have commercial uses.