Basically, this is everything that didn't fit in elsewhere, either because its focus is sufficiently broad, or narrow , or far enough from a main stream to exclude it from any one category.  Some are here because they fit multiple categories equally well (yet still refuse to blend with any)... and maybe a few books listed elsewhere could have as easily landed here...  Fan produced volumes are near the end of the page.
All Else

The Individuated Hobbit: Jung, Tolkien, and the Archetypes of Middle-Earth

Houghton Mifflin, Timothy R. O'neill

1979 Hardcover   ISBN : 039528208X

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Evocation of Virgil in Tolkien's Art :
Geritol for the Classics

Bolchazy-Carducci, Robert E. Morse

1986 Softcover   ISBN : 0865161763

1987 Hardcover   ISBN : 0865161755

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0865161763
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0865161755

A Question of Time :
J.R.R. Tolkien's Road to Faerie

Kent State University Press, Verlyn Flieger

1997 Hardcover   ISBN : 0873385748

2001 Softcover   ISBN : 087338699X

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0873385748
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Unsung Heroes of The Lord of the Rings :
From the Page to the Screen

Praeger Publishers, Lynnette R. Porter

2005 Hardcover   ISBN : 0275985210

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The Science of Middle-Earth

Souvenir Press Ltd.,  Henry Gee

2005 Softcover   ISBN : 0285637231

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Ents, Elves, And Eriador :
The Environmental Vision of J. R. R. Tolkien

University Press of Kentucky, Matthew T Dickerson & Jonathan Evans, Forwards by John Elder & Tom Shippey

2006 Hardcover   ISBN : 0813124182

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0813124182

Tolkien And Shakespeare :
Essays on Shared Themes And Language

McFarland & Co.,  Janet Brennan Croft (Editor)

2007 Softcover
ISBN-10 : 0786428279   |  ISBN-13:  978-0786428274

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0786428279

The Plants of Middle-Earth :
Botany And Sub-creation

Kent State University Press, Dinah Hazell

2007 Hardcover   ISBN : 0873388836   9780873388832

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Fan Stuff

A Tolkien Scrapbook : Stories, Poems, and Illustrations Celebrating the Author and His World

Grosset & Dunlap, Alida Becker, Editor

1978 Hardcover   ISBN : 0448164558

Running Press

1978 Lib. Binding   ISBN : 0894710834

1979 Softcover   ISBN : 0894710826

A Tolkien Treasury : Stories, Poems, and Illustrations Celebrating the Author and His World

Running Press/Courage Books
Editors W.H. Auden, Alida Becker, Michael Green & Daniel Grotta, Ill. Hildebrants, Tim Kirk

1989 Hardcover   ISBN : 0894717049

2000 Hardcover   ISBN : 0762409940

Miniature Edition

2001 Hardcover   ISBN : 0762409800

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0448164558
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0894710826
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0894717049

Meditations on Middle Earth

St. Martins Press, Karen Haber (Editor), John Howe

2001 Hardcover   ISBN : 0312275366

2002 Softcover   ISBN : 0312302908

Earthlight New Edition

2003 Softcover   ISBN : 0743468740

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0312275366
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0312302908
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0743468740

The People's Guide to J.R.R. Tolkien

Cold Spring Press, TheOneRing.Net, Erica Challis (Editor)

2003 Softcover   ISBN : 1892975904

More People's Guide to J.R.R. Tolkien

2004 Softcover   ISBN : 1593600267

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1st cover?
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1892975904
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1593600267