GuteBooks includes books from various sources, including Project Gutenberg, Google, and OpenLibrary.org. These works are in the public domain, and are totally free. That means that you won't find this year's new releases, but you will find the best literature of past years. Indeed, while many of the titles are the same ones you would find on a Kindle or a Nook, they are not just cheap, but entirely free.
Gutebooks allows you to view eBooks in two ways - by viewing the original pages of the scanned books, or by viewing resizable text scaled for your screen. Choose whichever method is best for you from the options menu.