I stumbled across this site the other day, and found myself bookmarking one site after another. This page is well organized, easy to navigate, and has a nice variety.
This site is also fantastic; although there is alot to take in. The setup is a little "busy" for my taste, but there is some great stuff here.
"Welcome to the World Wide School. The best place on the Internet to learn just about anything. Just read, click and learn. We wish you the best. This site is dedicated to the collection, preservation and presentation of educational material." (from about us section)
Those of you who are familiar with the Gutenburg Project will find this site sits right along those same lines. Enjoy the gems in this site!