I really hope Oyster has this service for e-books figured out:

The app’s design is important, but if the content isn’t there, a service like this won’t work. So the key thing is that Oyster has the books: Over 100,000 in-print titles, plus public-domain titles that are not included in that 100,000 figure.

A warning: You will not find hot new bestsellers here. But you will find real books that you have heard of, published within the last decade, from publishers that you have heard of (if you follow that sort of thing)