google also do a reader app - google books,that can work both online & offline. Overdrive is another free reader app that gives you access to library book on most tablets- sign up with your local library for e-book loans
Amazon do an kindle for android app for their store , As do Kobo for theirs.
So much choice
Wikipedia is usually a good place for comparisons & there is a very detailed table here:
http://en.wikipedia.org/wiki/Compari...eader_software