Encyclopedias

Annals of Arda
Glossary of the names, places, objects and thoughts of Middle-earth.
http://www.annalsofarda.dk/

BobMoCo Middle-Earth Glossary
Glossary of names, places and other terms for The Hobbit, Lord of The Rings, The Silmarillion and Unfinished Tales.
http://web.ukonline.co.uk/rwf.downing/index.htm

The Electronic Tolkien Encyclopedia Project:
Scholarly articles submitted by visitors about Middle-earth topics.
http://www.tolkienonline.de/etep/

Encyclopedia of Arda
An evolving encyclopedia, complete with illustrations, maps and an interactive chronicle.
http://www.glyphweb.com/arda/

From Middle-earth to Mithlond
Dedicated to the life and works of Tolkien.
http://www.btinternet.com/~p_cooper/index.htm

Galadriel Worshippers' Army
Listings and detailed information for the major female characters.
http://www.galadriel.org/

The Thain's Book
Descriptions of the people, places and things of Tolkien's Middle-earth in The Hobbit and The Lord of the Rings.
http://www.tuckborough.net/

Tolkien Encyclopedia: Interactive Edition
Read and publish entries to this listing.
http://www.geocities.com/Area51/Shire/3887/

Tolkien Gateway
A J.R.R. Tolkien encyclopedia.
http://tolkiengateway.net/

Wikipedia: Middle-earth
Article with sections on the continent's geography, peoples, languages and history.
http://en.wikipedia.org/wiki/Middle-earth