He is definitely one to read "in order of publication":
1. The Hobbit
2. LOTR
3. Silmarillion (if you loved The Hobbit and LOTR)
4. Unfinished Tales
5. Children of Hurin (damn, that's a tragic tale worthy of Wagner!)
6. History of Middle Earth (all 12 volumes, for serious fans and scholars only).
If I may -- I'd refine this a little. Here I focus just on Tolkien's work related to Middle-earth, but the short independent tales Farmer Giles of Ham and Smith of Wootton Major are perfect literary works in their own right, etc.
1. The Hobbit
2. LOTR
3.The Adventures of Tom Bombadil, a collection of poems with a mock-scholarly preface; several of the poems, such as "The Sea-Bell," are real gems
4.Tolkien's translations and commentary on [FONT="]“Nam[/FONT][FONT="]á[/FONT][FONT="]ri[/FONT][FONT="]ë[/FONT][FONT="]” and “A Elbereth Gilthoniel" at the back of The Road Goes Ever On (1967) -- here were tantalizing glimpses of things relating to The Silmarillion (1977); also, one might like to look over, at least, the treatise on the Nomenclature in The Lord of the Rings that is printed in Hammond and Scull's The Lord of the Rings Reader's Guide; the treatise was prepared by Tolkien to aid translators and contains some interesting nuggets
5.The Silmarillion
6.Unfinished Tales
7.Children of H[/FONT]úrin
8.History of Middle-earth series; I particularly recommend the following volumes:
a.Sauron Defeated -- for Tolkien's longest unfinished work, The Notion Club Papers. In the year 2012, in an Oxford basement, minutes of a dons' discussion group are found. They begin with a symposium on science fiction, then proceed to a weird tale about intergenerational memories of the downfall of Númenor. JRRT worked on this during a hiatus in the composition of LOTR.
b.The Lost Road -- a shorter unfinished romance also dealing with intergenerational memories or dreams
c.Morgoth's Ring -- for interesting late private papers on topics such as the origin of Orcs, and, notably, a poignant masterpiece,
Athrabeth Finrod ah Andreth.