e-books
Kindle Popular Classics "hundreds of thousands" of free or cheap e-books from Amazon
HathiTrust Over 3 million works available as full-text e-books
Internet Archive over 15 million free e-books to read and download
Open Library over 2.3 million e-books
Project Gutenberg over 57,000 free e-books
audiobooks
LibriVox free, public domain audiobooks