Science 
How Stuff Works
How Everyday Things Are Made
Chemical Elements
Science: Interactive Body

Science Fair Project Ideas
IPL Kidspace: Science Fair Project Resource Guide
Science Fair Central

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

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

Ecology
Ecoworld
Regional Trends . . .Grasslands
UN Atlas of the Oceans
Bioimages

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

Mathematics
Ask Dr. Math
The Math Forum@Drexel: Arithmetic

Fractions
Hyperstat Online 
Math.com
Math2.org
S.O.S. Math:  Fractions
Teach R Kids Math
Virtual Math Lab: Math Refresher
West Texas A&M Virtual Math Lab

Solar System/Stars
Journey through the Galaxy