Here are two lists of e-books being made freely available on-line. Please add more in the comments!
This is a list of academic presses making their books and research freely available.
Jim C. Hines' list of Free and Legal Science Fiction and Fantasy
Hines has collected a list of authors providing their work online for free.
Naturally, your public library is a great resource and the Libby app is my best friend for e-books. We will also find that the public library gives incredible access to movies, music, and periodicals via the series of tubes we all know and love.