Science & Math

How Stuff Works
http://www.howstuffworks.com/
Learn how everything works -- from SPF in sunscreen, to Patriot missiles!

Astronomy

NASA
http://www.amnh.org/rose/

The Nine Planets - A Multimedia Tour Of The Solar System
http://seds.lpl.arizona.edu/nineplanets/nineplanets/nineplanets.html

Biology

EMBL Reptile Database
http://www.embl-heidelberg.de/~uetz/LivingReptiles.html

Endangered Species
http://eelink.net/EndSpp/

Kimball's Biology Pages
http://www.ultranet.com/~jkimball/BiologyPages/

Plants Database
http://plants.usda.gov/

Chemisty & Physics

American Chemical Society: for educators and students
http://www.chemistry.org/portal/a/c/s/1/educatorsandstudents.html

General Chemistry Online
http://antoine.frostburg.edu/chem/senese/101/index.shtml

Periodic Table of the Elements
http://pearl1.lanl.gov/periodic/default.htm

The Laws Of Physics
http://www.alcyone.com/max/physics/laws/

Earth Science

National Geographic
http://www.nationalgeographic.com

National Oceanic and Atmospheric Administration
http://www.noaa.gov

Savage Earth
http://www.pbs.org/wnet/savageearth/

Savage Seas
http://www.thirteen.org/savageseas/

The Earth Fact Sheet
http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html

Math Sites

Convert it!
http://www.sciencemadesimple.com/conversions.html

How Many? A Dictionary Of Units Of Measurement
http://www.unc.edu/~rowlett/units/

Internet Mathematics Library
http://forum.swarthmore.edu/library/

Webmath
http://www.webmath.com

Science Projects

IPL Science Fair Project Resource Guide
http://www.ipl.org/youth/projectguide/

Science Fair Central
http://school.discovery.com/sciencefaircentral/