I know the Kindle's been available for Droid-equipped phones for a while now. Barnes & Noble has finally jumped on the bandwagon with an Android app — essentially 'Nook for Android.'
It installed on my HTC Incredible without a hitch, synced up with my B&N purchase list, but doesn't download the actual books unless you tell it to do so. It has 8 different fonts for reading and 5 different sizes, but the defaults worked well for me, other than making it one step smaller. I didn't even need to read the instructions to guess that page turning was with a single finger-flick one way or the other. If you tap a page, a slider comes up that lets you move quickly through the book, and tells you what page you're on. To bookmark a page, touch the upper right corner and it folds down just like a dog-ear. From the menu, you can go anywhere in the contents or your bookmarks. It appears the program remembers your last position in a book when you go back to it (need to test this some more).
The page-turn animation is kind of cool — it looks as if the edge of the page is under your finger or thumb, and you can partially view both the current and next/previous one. Or, if you do a quick flick, it just jumps by. (For those who don't like this, you can change it to a slide, but from the library view, not while reading a book. I like the animation better.)
The Nook Droid reader also supports automatic portrait/landscape viewing.
The only lack I noticed was the inability to add other non-B&N books, as I can on the actual Noon device… and with that one, I still have to say that segregating my two libraries has been a less-than-desirable aspect. Of course, my phone came with Adobe PDF reader software already installed, and it was easy enough to get FBReader and WordPlayer free from the Droid Marketplace to read ePub books.