One group that provides a free, vast library of works in the public domain (works that are old enough to no longer be copyrighted) is the gutenberg project http://www.gutenberg.org

If you feel passionately about free ebooks and have an hour to spare a month, one way to help keep this project alive is to volunteer as a proof-reader. It's painless.

I have had an ebook reader since the rocket ebook came out and I discovered the gutenberg project back when I got my rocket ebook. (My rocket ebook is still my primary ebook reader--I love it. I can take a relatively small device with me when I travel and carry approximately 30 books in it, depending on the size of the books that I'm storing).