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 Letters of Beethoven

Author: Emily Anderson
3 volumes
St. Martins' Press,1961.

Beethoven's Letters

Author: A. C. Kalischer
Translator: J. S. Shedlock
Editor: A. Eaglefield-Hull
Dover Publications
426 pages - 1972
ISBN: 0486227693.

Beethoven: Letters, Journals and Conversations

Author: Michael Hamburger
Thames & Hudson
1992
ISBN: 0500273243.

Heiligenstädter Testament

A copy of the Testement with accompanying texts (in numerous other languages)
Text: Ludwig van BEETHOVEN
Verlag Beethoven-Haus Bonn
1999
50 pages.

Heiligenstädter Testament

A copy of the Testement with accompanying texts
Text: Ludwig van BEETHOVEN
Weiner Beethoven-Gesellschaft
1976
12 pages.

Beethoven Tagebuch

A copy of the Testement with annotations and accompanying texts
Text: Ludwig van BEETHOVEN
Author: Maynard SOLOMON
v. Hase & Koehler Verlag
1990 - 196 pages
ISBN: 3-7758-1172-9.

Letters by or about Beethoven
Author: Richard BENZ
R. Piper & Co, München
1946
81 pages.

Die Stammbücher Beethovens

Zwei Blätter aus seinem Tagebuch

Ein Brief von Beethoven Grossneffen aus dem Jahre 1875

Aus der Sammlung Wegeler