What are some free books available in the ibooks app?

I am getting an iphone 4. I am excited, but I have to wait for the July shipment. I am super excited about the ibooks app. I know all about Project Gutenberg and the clic books (Mark Twain, Shakespeare, Poe, etc) that will be available on ibooks for free as well as the pre-loaded Winnie the Pooh collection (very cool). However, I have read that ibooks has lots of other free books. Does anyone know what other books you can get for free on ibooks? Also what are the cost of regular books as compared to buying the actual book?