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

Beethoven: Biography of a Genius

A reference biography in English
Author: George R. MAREK
Funk & Wagnalls, NY,
1969
696 pages.

Beethoven

The 1970 edition is the best version, but abridged newer versions are also available
Author: H. C. ROBBINS LANDON
The World of Art Library
Music - Arts book Society
1975 - 216 pages.

Beethoven: Impressions by His Contemporaries

Author: Oscar SONNECK
Dover, 1967 - reprint from 1927.

Beethoven and his world

Author: Scott BURNHAM
Princeton University Press
350 pages - 2000
ISBN: 0691070725.

Beethoven: His Spiritual Development

Author: J. W. N. SULLIVAN
Mentor 1949,
or Vintage Books, 1960.

Life of Beethoven

A reference biography in English
Author: Alexander Wheelock THAYER
Revised and edited by Elliot FORBES
Princeton University Press - 1967 - 1 141 pages
Two volumes - ISBN: 0-691-02717-X and 0-691-02718-8.

Beethoven and the Construction of Genius: Musical Politics in Vienna, 1792-1803

Work about Beethoven's first years in Vienna
Author: Tia DENORA
University of California Press
32 pages - 1996
ISBN: 0520088921.

Ludwig van Beethoven

Short biography and long presentation of works. Superbly illustrated!
Author: Joseph SCHMIDT-GORG
New York: Praeger
1970.

Beethoven

A great work by a clever scholar
Author: Romain ROLLAND
Freeport, N.Y.: Books for Libraries Press
1969.

Beethoven : The First Biography, 1827

If you want to read the very first biography, here it is
Author: Johann Aloys SCHLOSSER
Editor: Barry COOPER
Translator: Reinhard G. PAULY
Amadeus Press
1996 - 196 pages
ISBN: 1574670069.

Beethoven

Almost a reference, but questionable biography
Author: Maynard SOLOMON
Publisher: Schirmer Books
554 pages - 2001 (2nd revised edition)
ISBN: 0825672686.

Life of Beethoven

Ancient reference biography
Author: Louis NOHL
Traduction by John H. LALOR
A.C. McClurg & Company
Collection: Biographies of Musicians
1888 - 201 pages.

Beethoven, a Victorian Tribute

Based on the papers of Sir George Smart
Author: Percy M. YOUNG
Bobson Books
1976 - 125 pages
ISBN: 0-234-77672-2.

Ludwig van Beethoven - An Illustrated Biography

Magnificent illustrated biography (also exists in German)
Author: Ernst HERTTRICH
Verlag Beethoven Haus Bonn
1999? - 112 pages
ISBN: 3-88188-060-7.

Beethoven, The Composer as Hero

With numerous illustrations
Author : Philippe AUTEXIER
New Horizons
1992 - 144 pages
ISBN : 0-500-30006-2.

Ludwig van Beethoven

Biography of the composer
Author: LA MARA
Breitkopf & Härtel, Liepzig
1912
116 pages.

Ludwig van Beethoven, sein Leben in Bildern

Beethoven's life in pictures
Author: Richard PETZOLDT
Veb Bibkiographisches Institut
Leipzig - 1952
80 pages.

Volksbücher der Musik: Ludwig van Beethoven

With 21 pictures
Author: Gustav THORMÄLIUS
Verlag Velhagen & Klasings Volksbücher Nr. 7
1912 ?
34 pages.

The Beethoven Compendium

A very good reference book
Author: Barry COOPER
Thames and Hudson
1991
ISBN: 0-500-27871-7
350 pages.

The Beethoven Encyclopedia, his life and art from A to Z

Remarkable reference dictionary
Author: Paul NETTL
Citadel Press
1994 - ISBN: 0-8065-1539-2
325 pages.

Beethoven and his world - A Biographical Dictionary

Up-to-date reference dictionary
Author: Peter CLIVE
Oxford Unversity Press
2001 - ISBN: 0-19-816672-9
490 pages.

The Beethoven Companion : a comprehensive guide to Beethoven, his life and work

A chronological presentation made from extracts of other books written by various authors from Anton Schindler to Romain Rolland and many more
Authors: Thomas K. SCHERMAN and Louis BIANCOLLI
Doubleday & Company
1972 - 1,230 pages.