Not too long ago, Android went through a rebranding with their app marketplace. Once called the Android Market, it was changed to the Google Play Store. How you play books, we're not really sure. One thing that's been available with the App Store on iOS are iTunes gift cards. They make for a nice gift with the hundreds of thousands of apps available, and anything else you want to buy in iTunes.
It seems that Google Play gift cards will be launching soon after some photos leaked. Android Central received a few pics of Google Play gift cards available in $10 and $25 and are clearly branded as such. Whether you want music, movies, apps, or even books, the gift card will work with anything available in the Play Store.
As of right now, there is no word on when and where they'll be available. It would be pretty safe to assume that they'd be available online as well as in popular retail stores such as Best Buy, Target, Wallmart, and others. Google has never made money from phones and tablets directly, but indirectly through mobile advertising and their marketplace of apps, movies, books, music, etc.
They are a bit behind launching gift cards, but I guess now is better than never. Have a friend or family member who uses Android? Here's a potential present for the holidays. You do know there's only a few months left to shop, right? :-)