http://dhammacenter.org/media-download/e-book/
https://buddhismforbeginnersgroup.wordpress.com/category/dhamma-books-library/
http://www.buddhanet.net/ebooks_s.htm
Buddhadasa Bhikkhu: http://www.bia.or.th/en/index.php/2013-10-23-08-26-28/ebooks
https://tisarana.ca/teachings-audio/books-2/