Encyclopedias

HighBeam Encyclopedia - Offers articles from the Columbia Encyclopedia and Britannica Concise Encyclopedia.
http://www.encyclopedia.com/

Britannica Concise - Featuring 28,000 short articles.
http://concise.britannica.com/

Knol - Peer-reviewed encyclopedia from Google. Articles are written by named contributors.
http://knol.google.com/

Encyberpedia - Electronic encyclopedia with its own content as well as over 10,000 links to the best reference sites on the Internet.
http://www.encyberpedia.com/cyberlinks/links/index.html

Wikinfo - User edited encyclopedia based on Wiki software. Contains articles, information on editing, and a list of differences between this encyclopedia and Wikipedia.
http://www.wikinfo.org/

Encyclopaedia Britannica Online - Provides complete text of Encyclopaedia Britannica with search capabilities, related links, and multimedia enhancements. Full text for subscribers only; free trial available.
http://www.britannica.com/

How Stuff Works - Articles explain how hundreds of things work, from elements of the human body to space-age technology.
http://www.howstuffworks.com/

Hutchinson Encyclopedia - "A subset of the content (concise set) is provided for free, the access to the rest of the Hutchinson Encyclopedia requires subscription."
http://encyclopedia.farlex.com/

World Book Encyclopedia - Online version of the complete reference work along with dictionary, atlas, links, magazines, historical documents, audio, video, images, and 3D photographs. Requires free temporary registration with option to buy continued access for full articles.
http://www.worldbook.com/

Wikipedia - A free encyclopedia with millions of articles contributed collaboratively using Wiki software, in dozens of languages.
http://wikipedia.org/

Bartleby.com - Includes the Columbia Encyclopedia, Sixth Edition, dictionaries, and thesauri.
http://www.bartleby.com/

Classic Encyclopedia - Browsable online version of the 1911 edition of the Encyclopaedia Britannica.
http://www.1911encyclopedia.org/

Online Encyclopedia - Offers articles from on the 11th edition Encyclopedia Britannica, and from the Crystal Reference Encyclopedia. All articles are searchable and alphabetized.
http://encyclopedia.jrank.org/

Simple English Wikipedia - User-contributed online encyclopedia intended for people whose first language is not English.
http://simple.wikipedia.org/

Nuttall Encyclopædia of General Knowledge - Approximately 14,000 entries on topics including art, geography, literature, philosophy, religion. Originally published in 1907.
http://www.fromoldbooks.org/Wood-NuttallEncyclopaedia/

Encyclopedia Smithsonian - Links to on-line Smithsonian resources and answers to frequently asked questions from A to Z.
http://www.si.edu/Encyclopedia_SI/

Information Please - Online dictionary, Columbia Encyclopedia, and almanac reference.
http://www.infoplease.com/

The Probert Encyclopaedia - Reference source with entries covering a broad variety of subjects.
http://www.probertencyclopaedia.com