According to Gizmodo the Bible is the most represented book app on the iPhone. There are 1000+ versions to choose from (see the infographic below for a comparison with other classics.
“The Holy Bible has more than a thousand applications at the App Store. We counted up to 1001, but it was too boring to keep on going. Of those copies, not all were free. Some of the most popular works also have multiple copies, some are free, some are paid. Pride and Prejudice is one of the most popular, with 48 copies, seven of them available for a few rupees. Dracula has 34, five being paid copies for whatever reason. And so on.”