7 links
Encyclopedia of Arda
glyphweb.com
An evolving encyclopedia, complete with illustrations, maps and an interactive chronicle.
Galadriel Worshippers' Army
galadriel.org
Listings and detailed information for the major female characters.
The Electronic Tolkien Encyclopedia Project:
tolkienonline.de
Scholarly articles submitted by visitors about Middle-earth topics.
The Thain's Book
tuckborough.net
Descriptions of the people, places and things of Tolkien's Middle-earth in The Hobbit and The Lord of the Rings.
Wikipedia: Middle-earth
en.wikipedia.org
Article with sections on the continent's geography, peoples, languages and history.