University of Adelaide Press
https://www.adelaide.edu.au/press/titles/
Free PDF's are available for all titles.
The Rockefeller University Press
http://books.rupress.org/
A number of science oriented books are free in your choice of ebook format although you do need to go through the regular check-out.
Leuven University Press
http://upers.kuleuven.be/en/free-ebooks?
Offers a large number of free books in a number of languages in PDF format. Several books are collections of papers and essays in multiple languages.
OAPEN Library
http://www.oapen.org/search?browse-all=yes is a collection of open access books from a number of publishers (includes non-English books).