Tolkien Sites / Commercial Sites
Lord of the Rings Fanatics Site - For & By Tolkien Fanatics. The "Plaza" and the "Forum" should not be missed when paying a visit there, also there's a quiz if you would like to test your Middle-earth knowledge.
OneRing - The complete guide to Tolkien online
The Tolkien Shop, especially the "Works by Tolkien" page and the "Works about Tolkien" page  make for a worthwile visit. And while you're there you could check out the links  too.
Down per 2004-05-20, recheck! TolkienOnline.com
Down per 2004-05-20, recheck! TolkienWorld.com
lotrmaps.com and tolkienion.com: Both sites were closed due to Copyright issues in spring/summer 2004 and they may or may not be re-opened 
the Lord of the Rings.com The owner hosts currently 2 BBS sites, a "Forum", which is mostly free of advertising material and still worth a visit and a Role-Playing site.
The Barrow-Downs Especially the "Forum" is a "High-quality" place with quite some Tolkien experts around, especially the "Revised Silmarillion"-project deserves attention.
FolderTolkienSites ToDo: recheck broken links