Advanced Physics Forums (Popularity: )
http://www.advancedphysics.org Intended primarily for physics majors, graduate students, postdocs and faculty. Get meeting information, theoretical and research information and exchange of ideas. Meant for the physics community throughout the world.
ActaPhysica (Popularity: )
http://www.actaphysica.com/ Free social networking platform for the physics community, enables users to network with peers in the worldwide physics community and share knowledge, ideas, problems and resources.