Dictionaries and other Word Tools

American Heritage Dictionary
Research-It - Your one-stop reference desk, dictionaries, thesauri, translators.
Roget's Thesaurus
Roget's II: the New Thesaurus, Third Edition
Rhyming Dictionary
Webster's Dictionary
Word Central - Dictionary and Word Games
 

Encyclopedias

Encarta Online
Free Internet Encyclopedia
Encyclopedia.com
 

Literature

Knowledge Rush - Great works of literature and historical documents online - free for the reading.

Maps and Atlases

Atlapedia Online - Atlapedia Online contains full color physical and political maps as well as key facts and statistics on countries of the world.
MapMachine @ nationalgeographic.com - a wonderful collection from the world famous National Geographic Society.
World Atlas.com
World Fact Book - The CIA's Educational Website
 
Research Tools
 
Yahooligans
Helpful Web Pages from City Terrace Elementary's Web Site

NASA Kids
askjeevesKids
PBSKids
National Geographic
abcNews Kids