Tolkien reference

The Encyclopedia of Arda
http://www.glyphweb.com/arda/
What it says, covers all aspects of Middle-Earth

Ardalambion
http://www.uib.no/people/hnohf/index.html
An excellent series of pages on Tolkien's languages

Lalaith's Middle-Earth Science Pages
http://rover.wiesbaden.netsurf.de/~lalaith/M-earth.html
Despite the title, this pages focuses on the history of Middle-Earth; there's also an article about projecting the map of Middle-Earth on to the map of Europe.

Suite 101's Tolkien and Middle-Earth pages
http://www.suite101.com/welcome.cfm/tolkien
These pages contains some of Michael Martinez's Middle-Earth essays, which are interesting, informative and humorous by turn.

Tolkien message boards

IGN Vault maintains a set of Tolkien message boards.

Developers Board: http://vnboards.ign.com/board.asp?brd=5043
For discussing issues related to the (supposed) development of the MEO game.

General Board: http://vnboards.ign.com/board.asp?brd=5042
For general Middle-Earth discussion.

The Stilted Pony: http://vnboards.ign.com/board.asp?brd=5045
A roleplaying board (we ran an epic story there during 2000).

Tolkien MUSHes

Elendor
telnet://mush.elendor.net:1893
The largest and most popular Tolkien MUSH, set in the Third Age just before the events of Lord of the Rings.

Akallabêth
telnet://akallabeth.pennmush.org:3175/
A smaller MUSH set in the late Second Age, before the downfall of Númenor. I recently started a Hillman character called Barzag on this one.

Beleriand
telnet://beleriand.mux.net:4739
A First Age MUX. I've not visited this one myself, but thought I'd include it anyway.