Encyclopedia Britannica

http://www.eb.com
A preview of Britannica Internet Guide. Search capabilities and nicely organized subject links.

Encyclopedia Smithsonian

http://www.si.edu/resource/faq/start.htm
Responses to frequently asked questions (FAQs) hierarchically arranged by topic. Includes many reading lists of recommended books.

Free Internet Encyclopedia

http://www.encyclopedia.com
Includes references to large subject areas (MacroReference) and specific subjects and facts (MicroReference). Cross-references between two sections. Some material very useful.

Webliography: A Guide to Internet Resources

http://www.lib.lsu.edu/weblio.html
Well-organized collection of Web resources, arranged by topic and sub-topic.