There are plenty of places where you can get ebooks. Project Gutenberg is great, but you'll find that as the book has to be out of copyright before you can publish it on the web without the authors permission they are all quite old books. If you want newer books, you will have to pay for them - www.fictionwise.com is a great site. My fave though, if you like Sci-Fi, is www.baen.com. They also have the advantage of having a number of books on their website that you can read for free.
Andy