Answers.com
Encyclopedia aggregator and one-stop-shop for academic information.

Britannica
Featuring 100,000 scholarly articles. Highly respected.

Catholic Encyclopedia
10,000 articles on Catholic history, interests, and doctrine.

Columbia
Columbia’s online encyclopedia offers 51,000 entries.

Computer Desktop Encyclopedia
Featuring 20,000 topics and 2,500 images. Search field at bottom of page.

EncyclopediaMythica
Premier encyclopedia covering mythology, folklore, and religion.

Encyclopedia of Life
Database of scientific information on and photographs of known species.

Encyclopedia of Philosophy
Hundreds of original contributions by philosophy experts and volunteers.

Encyclopedia of Symbols
2,500 western signs and ideograms grouped by graphic characteristics.

Encyclopedia Smithsonian
Online resources from the Smithsonian Institution.

Europeana
Digital collection of scientific and cultural texts, images, videos, and sounds.

Freebase
Open database of the world’s information.

How Stuff Works
Source for easy-to-understand explanations of how things work.

Medline Medical Encyclopedia (by ADAM)
Diseases, symptoms, injuries, and more with photographs and illustrations.

Reference.com
Encyclopedia aggregator. Sources include Columbia Encyclopedia and Wikipedia.

Scholarpedia
Peer-reviewed open-access encyclopedia written by scholars from around the world.
www.scholarpedia.org

Stanford Encyclopedia of Philosophy
Hundreds of refereed encyclopedia entries.

Who2
Encyclopedia of more than 3,000 famous people and fictional characters.

Wikipedia
Find more than 2,000,000 entries, written and edited by users.

World Book
Traditional encyclopedia in print since 1917. Subscription required.

World Digital Library
Archive of primary materials from cultures around the world.