Society for Amateur Scientists http://64.124.46.128/pop
Discussions and research projects of the members of the Society as well as guest contributors. Registration required to post; guest access available to browse.
The Science Forum http://www.thescienceforum.com/pop
Discussion topics include astronomy, cosmology, biology, chemistry, earth sciences, physics, social sciences, health, medicine, history, economics, business, engineering, computer science, math and environmental issues.