Subcategories:
Encyclopedias 
Online research tool for finding information resources on a variety of topics.
http://www.british-encyclopedia.com/
Based on The Concise Columbia Electronic Encyclopedia. Search by letter of the alphabet or keyword. Features "Today in History" and top searches.
http://www.encyclopedia.com/
3. Hot Fact
Fun facts and trivia about animal, health, sports, travel and more.
http://www.hotfact.com/
4. Wikipedia
Free content encyclopedia available in many languages. Edit an article or add your own.
http://www.wikipedia.org/
5. wiseGEEK 
Clear answers for a wide variety of common questions. Subject areas include science, manufacturing, health, technology, and crafts.
http://www.wisegeek.com/