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

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

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/

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

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

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

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

MSN Encarta Encyclopedia
Includes a world atlas, dictionary, thesaurus, multimedia collection, and homework tools.
http://encarta.msn.com/

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/

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/

The LoveToKnow Free Online Encyclopedia
Browsable. Based on the eleventh edition of the Encyclopaedia Britannica, first published in 1911.
http://www.1911encyclopedia.org/

The Probert Encyclopaedia
Reference source with several hypertext linked entries covering a broad variety of subjects.
http://www.probert-encyclopaedia.co.uk/

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/

Wikipedia
A free encyclopedia built collaboratively using Wiki software. (GNU Free Documentation License) and with over 1,000,000 articles. Note that because articles can be "vandalized," information on Wikipedia is not always accurate.
http://en.wikipedia.org/wiki/Main_Page

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/