More from the “paradox of abundance” domain…
Internet Archive Text area - almost 2 million free books and documents - Kindle formats included, via ".mobi" or ".prc" files or specifically labeled "Kindle."
Remember that the Kindle also directly reads .txt and PDF files although .prc or .mobi ones may be more readable in font size.
There are also areas of files with somewhat questionable value, but the main sub-collections include American Libraries, Canadian Libraries, Universal Libraries (Carnegie Mellon, governments of India, China, Egypt), Project Gutenberg (another access point) -- and there are recent contributions from The Library of Congress, UCLA Scanning Center's special collections, etc.).