Project Gutenberg offers over 38,000 free ebooks: choose among free epub books, free kindle books, download them or read them online.
I'm currently reading all the Barsoom books by Edgar Rice Burroughs. It's awesome.
Another publisher that I find to be extremely consumer-friendly is Baen Publishing. If you're into Science Fiction, they have a lot of titles for you. They also have a good sized free library. I strongly recommend books from the 1632 series, of which, you can down load the first few for free. These books are not DRM encumbered, because they do not believe their customers are thieves.
All? Or just the first five? The later ones are still under copyright in the U.S., and I thought that Gutenberg was pretty good about honoring copyrights.