Bill Nye is the famous television Science Guy. This site includes episode guides, web search, TV listings and news. There is a Demo of the Day to try simple science experiments at home.
The Exploratorium
http://www.exploratorium.edu
San Francisco's Exploratorium is a large museum dedicated to education. This site contains information about the museum, its programs and exhibits. It has links to other science sites and includes many "exhibits" right on the site.
Albert Einstein
http://www.pbs.org/wgbh/pages/nova/einstein
PBS's NOVA site about Albert Einstein. There is biographical information, explainations of relativity and its implications. There are other links to Einstein sites, teacher's guide and much more. Relatively speaking, this guy was really smart.
