This page lists all sorts of links related to science fairs:

http://www.hallbar.com/sciencecenter.html

Ask Dr. Math; information about numbers, and you can ask questions if you want to!

http://mathforum.org/dr.math/dr-math.html

Bill Nye the science guy has lots of cool ideas for experiments.

http://www.billnye.com/

Cells alive has neat pictures and facts about bacteria, blood cells, crystals and the immune system.

http://www.cellsalive.com/

Demonstrated experiments for all ages, designed to "whelm" students!

http://www.mcrel.org/whelmers/

School science fairs homepage from Newfoundland

http://www.stemnet.nf.ca/sciencefairs/

Virtual science fair page from Minnesota

http://www.isd77.k12.mn.us/resources/cf/welcome.html

Home page of the Exploratorium museum in San Francisco

http://www.exploratorium.edu/

Links to interesting experiments and a virtual body tour

http://www.madsci.org/labs/MAD_labs.html

Archive of experiments from the "yuckiest site on the Internet"

http://yucky.kids.discovery.com/flash/fun_n_games/category_icky.html