In fact, there are 30,000 free ebooks available, all from one site. Where, you ask??? Check out Project Gutenberg. From humble beginnings, this volunteer project has grown. Not only do they offer ebooks online, but also audio books, downloadable CDs/DVDs, and digitized sheet music. You'll also find links to a number of other sites which offer free ebooks.
Do they really have anything worth reading for free? How about William Shakespeare, Rudyard Kipling, or Jules Verne? Of course there are many, MANY more authors included on the site. I encourage you to take a few minutes to browse around and see for yourself all the great literature available to you.
You might be wondering, what do I need to read all this electronic literature? With formats including ePub, Mobipocket, HTML and simple text formats, you can read these on your PC, iPhone, Kindle, Sony Reader, other mobile phones, gaming system, mp3 player, or other portable devices. With that many options, you're sure to have access to at least one device capable of displaying these ebooks.
Project Gutenberg is a purely volunteer endeavor. You can help by donating, or check out the volunteering page for more information.