Houghton Mifflin First Edition 1950, Illustrated by Pauline Baynes.  Blue cloth cover (photo available), two color plates.  Because early impressions have no ISBN, it works best to search by date.  There were reportedly three printings prior to 1960.

Thomas Nelson & Sons 1961, Illustrated by Pauline Baynes

Houghton Mifflin 1965, Illustrated by Pauline Baynes
The 4th through 11th HMCo printings were produced jointly with George Allen & Unwin (UK), the final being the 11th in 1974, which had a list price of $6.95.  Early copies would of course not have an ISBN.

Houghton Mifflin 1978,  Illustrated by Pauline Baynes
Pictoral hardcover issued without dust jacket.  Print date not stated inside - 1976 copyright is the latest date present.  Two known printings, RRP $4.95

Houghton Mifflin Reset Edition 1991,  Illustrated by Roger Garland
Hardcover in dust jacket.  This identifies as a "First American Edition 1991", is more scarce than the Baynes illustrated edition, and very unfortunately, all the 1991 Garland illustrated Tolkien editions have poor paper quality.  These are actually library bound copies of a UK paperback edition.  Most have the publishing information on a label applied to the copyright page, but not all, and in my experience ex-library copies do not.  Printed in Great Britain.  First printings have a complete number line, no subsequent printings found.  RRP $13.95.

Houghton Mifflin 2000 50th Anniversary Expanded Edition
Hardcover in dust jacket, Illustrated by Pauline Baynes, edited by Wayne Hammond and Christina Scull.  This edition contains the original story outline and notes regarding a planned but never published sequel.  First printings with full numberlines found in priced and unpriced jackets.  Available new,  RRP $18.00 - $20.00

Harper Collins International Edition 2014
Hardcover pocket edition.  Illustrations by Pauline Baynes, edited by Wayne Hammond and Christina Scull.  There are matching editions of Smith of Wootton Major and The Adventures of Tom Bombadil, of course.  RRP $13.00

Houghton Mifflin First Edition 1967,  Illustrated by Pauline Baynes
Green cloth, very small hardcover, dust jacket.  Three known printings, original RRP $1.95.  The jacket is similar to the cover used for the first U.S. paperback (which also contained Farmer Giles of Ham - see below).

Houghton Mifflin Reset Edition 1978,  Illustrated by Pauline Baynes
Pictoral hardcover issued with no jacket.  Print date not stated inside - 1975 copyright is the latest date present.  Two known printings.  RRP $4.95

Houghton Mifflin Reset Edition 1991,  Illustrated by Roger Garland
Hardcover in GORGEOUS dust jacket.  This identifies as a "First American Edition 1991", is more scarce than the Baynes illustrated edition, and very unfortunately, all the 1991 Garland illustrated Tolkien editions have poor paper quality.  These are actually library bound copies of a UK paperback edition.  Most have the publishing information on a label applied to the copyright page, but not all, and in my experience ex-library copies do not.  Printed in Great Britain.  First printings have a complete number line, no subsequent printings found.  RRP $13.95.

HarperCollins 2005, Edited by Verlyn Flieger
Enlarged edition, containing much background on the story and a facsimile of hand and typed drafts.  Not produced in the U.S., but was widely available new online.

Harper Collins International Edition 2015
Hardcover pocket edition.  Illustrations by Pauline Baynes, edited by Verlyn Flieger.  There are matching editions of Farmer Giles of Ham and The Adventures of Tom Bombadil, of course.  RRP $13.00

Ballantine First PB Edition 1969, Illustrated by Pauline Baynes.  The ISBN does not appear in early printings;  it is deduced by taking the numbers printed on the spine, adding 0 (the region code) to the start, and replacing the 095 at the end (this is the price:  95 cents), with the missing check digit;  in this case, X.  Ten printings in this cover, 1969 - 1974

Ballantine, new cover art by The Brothers Hildebrandt, illustrated by Pauline Baynes.  Printings 11 through 15 have the red border.  RRP $1.50-$1.75

Ballantine PB Reissue 1977, cover by The Brothers Hildebrandt, illustrated by Pauline Baynes.  All 1986 and later printings share an ISBN.  Original RRP $1.75

Nelson Doubleday Book Club Edition,  illustrated by Pauline Baynes
Yellow or blue paper over boards;  yellow is more common and thought to be an earlier printing.  Beautiful jacket illustration by Daniel R. Horne.  The printing date is not stated, but the jacket art is dated 1983.  Copyright 1976 is the only date inside.  No ISBN, but it has been found listed under a UK ISBN, 0048230766.  This is the only hardcover version of this double title.

Ballantine PB Reissue 2003.  Available new,  RRP $6.99

Houghton Mifflin First Edition 1965
Dark blue or red cloth hardcover, jacket illustration by Robert Quackenbush.  At least 8 printings, early printings would have no ISBN,  RRP $4.00 - $9.95

Houghton Mifflin second edition 1989, includes the poem Mythopoeia.  Black cloth hardcover.  "Tree of Amalion" by Tolkien stamped in copper on green jacket.  Three known printings, very pretty book, and rather scarce.  Original RRP $12.95