To even farther diversity their product line, Google have now added an eBook library to the Android Google Market. To access the library, press the "Books" menu inside the market app. This feature is currently available to US customers only. Just like apps, the user can also return the book within a period of time if it does not meet expectations.
Also note that the eBooks purchased can be viewed in any eReader app and/or purchased using the web-based Android Market using the users Google Account. The web-based purchase can then be transferred to any Android devices associated with that Google Account.