This list of works is by no means exhaustive. It contains just those of which I know, and those which have been pointed out to me. Books in French are here.

Thank you to Gail for her help

The New Hess Catalog of Beethoven's Works

Update of the Hess catalog with all the 401 works (with corrections, and comments)
Author: James F. GREEN
Vance Brook Pub
310 pages - 2003
ISBN: 0964057034.

The Cambridge Companion to Beethoven

Remarkable work
Authors : Glenn STANLET - Barry COOPER and others
Cambridge University Press
2000 - 268 pages
ISBN: 0-521-58934-7.

Beethoven Quartets

Author: Joseph KERMAN
W.W. Norton & Company
1979 - 386 pages
ISBN: 0393009092.

Beethoven and His Nine Symphonies

Author: George GROVE
New York: Dover Publications
1962 - 3rd edition
407 pages
ISBN: 0-486-20334-4.

Critical Study of Beethoven's Nine Symphonies

Author: Hector BERLIOZ
University of Illinois
200 pages - 2000
ISBN: 0252069420

Beethoven's Ninth - A political History

Author: Esteban BUCH
University of Chicago Press
244 pages - 2003
ISBN: 0226078124

Wagner and Beethoven : Richard Wagner's Reception of Beethoven

Musical study
Author: Klaus KROPFINGER
Translator: Peter PALMER
Cambridge University Press
1991 - 288 pages
ISBN: 0521342015.

Beethoven

Musical study and biography
Author: Paul BEKKER
Translator: M. BOZMAN
Dent's International Library of Books on Music
1925 - 392 pages.

Beethoven's Sketches - An analysis of his style based on a study of his scketch-books

Author: Paul MIES
Translator: Doris L. Mackinnon
Dover Publications
198 pages
ISBN : 0-486-23042-2.

A Companion to Beethoven's Pianoforte Sonatas

Author: Donald Francis TOVEY
ABRSM Publishing
2004 - 308 pages.

Notes on the interpretation of Beethoven Sonatas

Author: J. Alfred JOHNSTONE
Allan & CO, Melbourne, Australia
1927? - 118 pages.

The Piano Quarterly

The Piano Quarterly - 24th year
Spring 1976 - Number 93
Pages 25 to 57.

Beethoven, Performers and Critics

The international Beethoven Congress, Detroit 1977
Authors:
- Michael STEINBERG: Writing about Beethoven
- Douglas JOHNSON: Music for Prague and Berlin: Beethoven's Concert Tour of 1796
- Eva BADURA-SKODA: Performance conventions in Beethoven's early works
- Otto BIBA: Cocnert life in Beethoven's Vienna
- James WEBSTER: Traditional elements in Beethoven's middle-period string quartets
- Karl-Heinz KÖHLER: The conversation books: aspects of the new picture of Beethoven
- Maynard SOLOMON: Beethoven and Schiller
- Robert WINTER: The sketches for the "Ode to Joy"
Edited by Robert WINTER and Bruce CARR
Wayne State University Press
1980 - 221 pages.

Beethoven's Folksong Settings

Chronology, sources, style...
Author: Barry COOPER
Clarendon Press - Oxford
270 pages - 1994
ISBN: 0-19-816283-9.

The Beethoven Journal (formely 'The Beethoven Newsletter')

Revue of scholarly studies
Author: The American Beethoven Society
Since 1986
ISSN: 1087-8262.