Missouri Botanical Garden http://www.mbgnet.net/index.html
Learn about one of North America's greatest ecosystems - the prairie http://www.bellmuseum.org/distancelearning/prairie/index.html#
X-Rays of the Human Body http://www.accessexcellence.org/RC/VL/xrays/
Fact Monster http://www.factmonster.com
Ask for Kids http://www.askforkids.com
National Geographic for Kids http://www.nationalgeographic.com/kids/