The Tolkien Shop, especially the "Works by Tolkien" page[4] and the "Works about Tolkien" page [5] make for a worthwile visit. And while you're there you could check out the links [6] too.
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 [7]
the Lord of the Rings.com The owner hosts currently 2 BBS sites, a "Forum"[8], which is mostly free of advertising material and still worth a visit and a Role-Playing site[9].
The Barrow-Downs Especially the "Forum"[10] is a "High-quality" place with quite some Tolkien experts around, especially the "Revised Silmarillion"-project deserves attention.