I’m interested in invented languages in general, not just Tolkien?
The CONLANG mailing list (http://groups.yahoo.com/list/conlang) deals with constructed languages. Other useful sites include Mark Rosenfelder’s Language Construction Kit, at http://www.zompist.com/kit.html, and the Langmaker site (http://www.langmaker.com/index.htm ). There is a Constructed Languages Webring at http://www.ifi.ntnu.no/~hannemo/sc/index.html, with links to many more sites.