Enchanted Learning http://www.enchantedlearning.com/subjects/astronomy/
NASA http://www.nasa.gov/audience/forstudents/5-8/features/index.html
Virtual Solar System http://www.nationalgeographic.com/solarsystem/ax/low.html?2d
Views of the Solar System http://www.solarviews.com/eng/
netTrekker http://school.nettrekker.com