The vast continent of published materials by and about J.R.R. Tolkien can be as daunting and perilous as Middle-Earth itself.  Here you will find many useful guides that will help you sort it all out and get you there and back again.  The Guide to U.S. Editions describes in detail all of the currently available editions of The Lord of the Rings, The Hobbit, The Silmarillion, Unfinished Tales, and the History of Middle Earth series.  There are also special pages dedicated to other Tolkien books, British editions, out-of-print editions, and a section for all of the audio editions, which explains the differences of the various audio books, dramatizations and archived recordings by Tolkien himself.  Another section lists works of world literature that were a major influence on Tolkien as he created his imaginary world.

Also of note here is the Guide to the Letters.  This guide indexes The Letters of J.R.R. Tolkien in the form of questions that are often asked by readers of his works.  Following each question are numbers of the letters which answer the question in Tolkien's own words.