Importance of the CMB in Cosmology. Filled with lots of links and other good stuff. Physlets Cool Java-powered physics demos. More cool demos and applets on modern physics stuff. Astronomy Calculator Check this out.
Microwave ovens Description of how microwave ovens work.
Satellite Orbits Shows current positions of satellites orbiting the earth and is updated every few seconds. Mass. Einstein Tour of Einstein's Life and work. Virtual tour of General Relativity and Black Holes Explanation of why Einstein's theory lead astronomers to posit the existence of black holes. You may be familiar with the proxy server. It allows free access to on-line publications.