General

How Stuff Works

A guide to the workings of things, from the mundane to the complex

Internet Public Library

The Internet Public Library, sponsored by the University of Michigan, provides links to educational sites in the arts, sciences, and other fields.

Anatomy

Gray's Anatomy of the Human Body

The unabridged, classic Gray's Anatomy of the Human Body includes nearly 1,300 etchings of body parts and systems

Archaeology

Cyber Pursuits

User-friendly index compiled by a Texas Web designer

Astronomy

Skymaps.com

Free monthly sky maps

Biology

The Biology Project

An overview of major topics

Chemistry

WebElements.com

A guide to the periodic table 

Dictionary

Merriam-Webster.com

A free dictionary/thesaurus from Merriam-Webster 

History

Metropolitain Museum

A work-in-progress timeline stretching from 20,000 B.C. to A.D. 1600

Literature

Gutenberg.net

Thousands of public domain books

Math

Algebrahelp.com

Edu4kids.com

Martin Dale Center

Psychology

Psychology.org

Writing

Bartleby.com

William Strunk Jr.'s classic Elements of Style (1918 edition)

World Facts

World Factbook

The CIA maintains this guide to countries, with information on their populations, governments, geography, agriculture, health systems, languages, etc.