Encyclopedia Britannica Over 40,000 articles. Includes links to other encyclopedias; law, science, biographies, surgery, small business, American industries, mental disorders, health and more.
Columbia Encyclopedia Full text from Barleby.com.
How Stuff Works Extensive, easy to navigate, easy to read.
Infoplease Accesses more than 57,000 articles from the Columbia Encyclopedia. Other info on the site; almanacs, atlas, dictionary, quizzes, timelines, country profiles, and lots more.
Encyclopedias for general reference, science, health, nature, humanties, places, cars, instruments, kids, and home improvement.
Medical encyclopedia from the U.S. National Library of Medicine and the National Institutes of Health.
Mythica, encyclopedia of mythology, folklore and religion from Pantheon.org.
Nolo legal encyclopedia.
Online encyclopedia by HighBeam Encyclopedia. Search through articles from Oxford University Press, Britannica, and Columbia Encyclopedia.
Smithsonian research, includes science & technology, conservation, history & culture, and art & design.
Wikipedia A great place to start.