Space Exploration
  Web Link
  Link   NASA
NASA's fantastic website.
  Link   European Space Agency
Official website of the ESA
  Link   SEDS
Students for the Exploration and Development of Space. A general site which tries to educate on the benefits of space. They host a lot of good educational resources including the Nine Planets and the Messier Deep Sky Catalog.
  Link   National Space Society
Our Vision: People living and working in thriving communities beyond the Earth, and the use of the vast resources of space for the dramatic betterment of humanity.