InfoPlease: This site provides access to more than 57,000 articles from the Columbia Encyclopedia, sixth edition.
Encyclopedia Smithsonian: This site answers frequently asked questions about the Smithsonian, with links to resources on subjects from Art to Zoology.
Encyclopedia.com: This online source provides more than 60,000 frequently updated articles from the Columbia Encyclopedia; each article is enhanced with links to newspaper and magazine articles, pictures, and maps. Includes over 100 encyclopedias and dictionaries.
Kpedia - Search over 700,000 articles in the Kiddle encyclopedia. All content from Kiddle encyclopedia articles (including the article images) can be freely used for personal and educational purposes under Attribution-ShareAlike license, unless stated otherwise.
The Elements of Style by William Strunk Jr. - online version of this classic reference book. Gives briefly "the principal requirements of plain English style and concentrates attention on the rules of usage and principles of composition most commonly violated."
eNature Fieldguides - fieldguides to over 5,500 North American plants and animals from the National Wildlife Federation.
Gray's Anatomy - Bartleby.com's edition of Gray's Anatomy of the Human Body features 1,247 vibrant engravings - many in color - from the classic 1918 publication, as well as a subject index with 13,000 entries.
How Stuff Works by Marshall Brain - from BYG Publishing, Inc.
Merck Manual of Diagnosis and Therapy, 17th edition - contains information on diseases, diagnosis, treatment and prevention for health professionals.
World Factbook - from the U.S. Central Intelligence Agency. Data for more than 260 countries. Includes the country map and flag, geographic, population, government, economic, communication, transportation, military, and transnational issue information.