The Virtual Laboratory
www.physicsweb.org/TIPTOP/V1AB

Periodic Table of the Elements
www.dayah.com/periodic

Web Elements and periodic table
www.webelements.com

Surfable Books
www.surfablebooks.com -acts as a science encyclopedia

Science.ca
www.science.ca/reference -major source for Canadian science

How Stuff Works
www.howstuffworks.com