Encyclopedia Mythica - http://www.pantheon.org/
An encyclopedia of mythology, folklore, and religion.
HowStuffWorks - http://www.howstuffworks.com/
Explains thousands of topics, from engines to lock-picking to ESP, with video and illustrations so you can learn how everything works.
Illustrated Encyclopedia of Endangered Animals - http://www.konicaminolta.com/kids/animals/index.html
An online illustrated encyclopedia of endangered animals that strives to inform and educate children about the danger of extinction of animal species due to environmental destruction.
Information Please - http://www.infoplease.com/
Provides and online dictionary and encyclopedia.
New World Encyclopedia - http://www.newworldencyclopedia.org/
Designed to organize human knowledge so the reader will learn information not just for its own sake, but for its value to the reader and the world as a whole.
The Encyclopedia of House Plants - http://www.gflora.com/
Find more than 300 various house plants with descriptions and pictures, botanical and common names, and instructions for cultivation and propagation.
World Christian Database - http://www.worldchristiandatabase.org
Provides comprehensive statistical information on world religions, Christian denominations, and people groups.