ActaPhysica - 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.

Advanced Physics Forums - 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.

Groupsrv.com - Physics Forum - Discussion for scientists.

Physics Forums - Bulletin boards on physics and related subjects. Includes related polls and a list of active threads.

PhysOrg Discussion Forum - Applied physics, nanotechnology, quantum physics, and semiconductor technology. Also discussions of the latest physics news.

QuantumBrain - Collaboration between a neuroscientist based at the University of Oxford and a quantum physicist based at the University of Queensland. Includes blogs and philosophical musings.

Scott Watson's Physics FAQs - A list of FAQs (Frequently Asked Questions) regarding Cosmology, String theory, Relativity and General Physics