WebPhys

Relativity FAQ: http://math.ucr.edu/home/baez/physics/relativity.html

Physics today online: http://www.aip.org/pt/

Cosmology: http://www.astro.ucla.edu/~wright/cosmolog.htm

Arxiv (an online repository of physics journal articles): http://arxiv.org/

CategoryWebsites? see GoodWebsites