General+Sites

Web Elements http://www.webelements.com/ Periodic Table with values for important chemical constants.

Mad Scientist http://www.madsci.org Ask a scientist any question. Also contains archives with many interesting responses. If you have ever wondered about it, you will likely find a quality scientific discussion on this site.

Molecule of the Month http://www.geocities.com/CapeCanaveral/Lab/5875/