Science/Mathematics

General Science 
How Stuff Works
How Everyday Things Are Made
How Products Are Made
Chemical Elements
Animated Periodic Table of the Elements
Interactives:  The Periodic Table
Science: Interactive Body
Science and Engineering Encyclopedia

Inventors
National Inventors Hall of Fame

Science Fair Project Ideas
IPL Kidspace: Science Fair Project Resource Guide
Science Fair Central
Experimental Science Projects: An Introductory Level Guide

Animals
The Animal Diversity Web
Animal Info: Information on Rare, Threatened 
and Endangered Mammals
enature.com Field Guides
North American Native Fish 
Smithsonian Institution: North American Mammals
SFWS Endangered and Threatened Species
U.S. Fish and Wildlife Service
USFWS National Image Library
WWF Wildfinder

Insects
Butterflies of North America
Butterflies and Moths of North America
Franklin Institute Online--Insect Hotlist

Ecology
Ecoworld
USGS Grasslands
UN Atlas of the Oceans
Bioimages
Encyclopedia of the Earth

Plants
Plant Information Online
The Victory Garden
Common Trees of Pennsylvania
enature.com Field Guides
Ecoworld:Trees

General Mathematics
Ask Dr. Math
The Math Forum@Drexel: Arithmetic
Fractions
Hyperstat Online 
Math.com
Math2.org
Online Mathematics Textbooks
S.O.S. Math:  Fractions
Teach R Kids Math
Virtual Math Lab: Math Refresher
West Texas A&M Virtual Math Lab

Algebra
Algebasics

Solar System/Stars
Journey through the Galaxy
Astronomy Online