Making a list of potentially important books out of print (in no particular order). Will update over time:
Monk and Mason on the Tigris Frontier: The Early History of Tur `Abdin by Andrew N. Palmer (1990)
The Raven of Zurich: The Memoirs of Felix Somary (1960, first published in German), (1986, First English Translation).
*The Mirror of History* bookset on Chinese Statecraft published in 1046 AD and presented to the Emperor of China. Translation into English pending, with forward by Ambassador Chas Freeman