Britannica Online is the online version of Encyclopedia Britannica and includes internet links.

Encyberpedia is an electronic encyclopedia with its own content as well as over 10,000 links to the best reference sites on the Internet.

Merck Manuals - Encyclopedic medical manuals

The Probert Encyclopaedia is a serious reference source with over 60,000 fully hypertext linked entries covering the entire spectrum of human knowledge, content is aimed at journalists and researchers.

Wikipedia This is an open-content encyclopedia produced by volunteers and is not peer reviewed. Contains more than 7,000,000 articles in several languages.