Not long ago Amazon released their Kindle eBook reader for Android which brought all of the titles purchased for the Kindle Reader (the device) to the Kindle Reader (the app).
I found it quite ironic that Kindle app came to Android before the Barnes and Noble NOOK app. Why? The NOOK (the device) is based on the Android OS, so the code for the eBook reader itself was already written. Why did it take so long for B&N to release their app for Android phones? Unfortunately, they're not commenting on that, so it's anyone's guess.
To make use of NOOK for Android you'll want to search for and download it from the Market (not to worry, it's free and works on Android 1.6+ devices). You'll also need a B&N account, which you can do from within the app over your data connection.
The interface is clean and simple. Just like Kindle, users can sync their reading progress across devices. Swiping the page left or right produces a very smooth page-turn animation that actually looks and acts like a physical page, which is a very nice touch. One of the features of the NOOK service is the ability to "lend" a copy of your book to a friend (just like a real book, how novel). According to B&N literature, they're the only eBook reader that allows lending.
The one thing that keeps me from jumping ship from Kindle is B&N's insistence on users providing them with billing information (including a credit card number) to be able to sync anything to the reader, even free titles. The only way around this requirement that I've found is to download the book directly onto the Android from within the NOOK app, but you're limited to the featured titles displayed by the app itself.