I’m enjoying the “Standard eBooks” site as a source for out-of-copyright books for eReaders et al.
It’s a similar concept to the fabulous Project Gutenberg et al.
The main difference is that Standard eBooks ensure the texts are first cleaned up in terms of typos, punctuation, design, typography and metadata. They also add eReader-supported features like tables of contents and footnotes that you don’t always see in free downloads.
All books are available in epub, azw3 (for Kindle), kepub and advanced epub formats. As a Kindle user, I found it easiest to email the epub version to my Kindle, now Amazon started supporting that file format.
You can volunteer to help or donate if you feel so inclined.