You might be interested in Bookmarking Wayne Hammond & Christina Scull's site (the Editors of the 50th Anniversary edition, as well as the writers of the recent Tolkien Companion & Guide & the LotR Reader's Guide ). Most useful part of the site is the
Addenda & Corrigenda section, which gives updates & corrections to the published books - there are some interesting additions & alterations to the above books given there. Worth checking out if you've bought them.