Project Gutenberg
you can find more than 50 000 free ebooks in gutenberg and they have books for amazon kindle epub and plain text utf and html. they have done a hard work digitizing these books for you and have the option to read these books online if you’re lazy to download books.
Manybooks
You can find over 33 000 free books on manybooks and you can browse by author , languages , titles, etc. the free books are well formatted for kindle, nook and many other ebook readers. there is a html version available for those who prefer to read books online without downloading
loyalbooks
Loyalbooks is previously known as books should be free and it has a very good collection of free audio books and ebooks. dont forget to check their top 100 books to see popular books to get the best out of their site. this site allows you to select books by genre, language , audio books can be played online if you’re not a fan of downloading mp3 files.