Good timing bumping this thread. There's a new Humble eBook
Bundle. Works the same as the game bundles pretty much. Pay what you want, get DRM free ebooks, pay more than the average and get some extra ones free. You choose what percentage of your money goes to the authors, which to Humble Bundle, and which percentage to charity. Books should work on pretty much any eReader. Current average purchase price is $11.59. So if you pay $11.60 or more, you get the bonus books as well.
The Humble eBook
Eight works of literary genius. Humble eBook Bundle features eight masterful works from a prodigious league of award-winning authors. Name your price and receive Pirate Cinema, Pump Six and Other Stories, Zoo City, Invasion: The Secret World Chronicle, Stranger Things Happen, and Magic for Beginners. Customers who beat the average will also receive Old Man's War and the graphic novel Signal to Noise!