This is my shortlist and an essential guide to the writings of J. R. R. Tolkien. I've decided to create this list because the various editions of Tolkien's work can be quite confusing, especially given the range of publications and even copyright scandals that Tolkien's work has experienced in the United States. There are a few works that at the moment only can be found in the UK but because they represent variations of Tolkien's books that cannot otherwise be found, I recommend them here. Also, I don't include links to booksellers because the information there can also get muddled.
1. The Lord of the Rings. 50th anniversary edition. 2005. paper. ISBN 978-0618640157
This is the edition to get. Forget picking up mass market paperback editions. Instead, you should find your way to this, the most accurate and essential edition of LOTR. Edited by W. Hammond and C. Scull, this edition finally corrects the text of tremendous error, provides corrected maps, and includes a full index. The introduction by D. Anderson tells the sorry history of the publication of the LOTR in the US. This version sets everything right. There are two higher grade bindings of this edition: I prefer the "deluxe edition" (ISBN 978-0544273443) which is better bound than the paper and more easily handled than the most expensive hardbound with slipcase (ISBN 978-0618517657)
2. The Hobbit. Cover by Peter Sis. 2001. Hardbound. ISBN 978-0618150823
There are other versions of the Hobbit available but this is the most readable and the most accessible to you and to younger Hobbits you may know. The 1973 hardbound with slipcase edition (ISBN 9780395177112) includes all of Tolkien's illustrations as well as the realization of his ideas for the cover illustrations. Interested readers of all of Tolkien's illustrations can find them collected in the excellent book The Art of the Hobbit, eds. W. Hammond and C. Skull (ISBN 978-0547928258).
3. The Silmarillion. Ed. Christopher Tolkien. 2nd. ed. Hardbound. ISBN 9780618135042
This is the book that Tolkien wanted to publish but never got to. Hobbits got in the way. Tolkien's unfinished writings on, in, and about Middle Earth exceed but include this fantastic book called the Silmarillion. This volume, edited by Tolkien's son Christopher Tolkien, includes the creation of Middle Earth (the amazing Ainulindale) and the downfall of the human civilization known as Numenor.
4. On Fairy Stories.
While planning a sequel to The Hobbit, Tolkien was invited to give a lecture about fairy stories. This essay was the result. It represents a significant reflection on aesthetics, ethics, and theology. It is essential to Tolkien. I love this essay so much it almost eclipses my love of the other writings!
The problem is that the best edition of this is unavailable in the US. Tree and Leaf (ISBN 9780007105045) contains the essay as well as the parallel poem on faerie "Mythopoeia." Older editions of this book can be found used but they are scarce. The cheapest way to get the essay is in the mass market paperback The Tolkien Reader (ISBN 9780345345066). You may find a better version of it included in the collection Tales from the Perilous Realm, 2008 (ISBN 9780547154114).
5. History of Middle Earth (12 vols) and Unfinished Tales. Various editions.
You should only start reading these things until after you have read the appendices to LOTR and the entire Silmarillion. The History of Middle Earth and Unfinished Tales are collections of various manuscripts and writings of Tolkien some of which Christopher Tolkien edited to create the Silmarillion. This is hard to wade through but worth every effort.
6. Artist & Illustrator, eds. W. Hammond and C. Skull. 2000. Paper. ISBN 978-0618083619.
A fine collection of Tolkien's art that either land the ground for his writing or was intended to accompany it. Essential to pondering the interaction of his text and visual art.
7. The Letters of J. R. R. Tolkien, ed. H. Carpenter. 2001. Paper. ISBN 9780618056996
Reflections on the Hobbits, their economy of birthdays, among discussions of evil, the relationships of characters, theological speculation, and ordinary human laments make these letters indispensable for any reader of Tolkien.