I've had a second generation Kindle for some time, but for the past 8 months or so I have been sampling eBooksellers different from Amazon, and unfortunately Kindle does not read anything but what comes from Amazon X-<.
Kindle for Android, Nook, Kobo and Google eBooks apps all run on a XOOM I happen to have. But when all I want to do is just to read, it is a bit too heavy, especially when I am horizontal facing the ceiling. Then recently I saw Barnes & Noble selling the "all new Nook", aka "Nook Simple Touch", which has a 6-in e-Ink display (the same size as the second and the third generation Kindle) and runs on Android 2.1, which was quickly followed by rooting instructions that allows applications to be side-loaded ;-)
Compared to the second generation Kindle, it is significantly smaller (the bottom fourth of Kindle is a keyboard which Nook Touch does not have) and lighter, but interestingly, I found out that the small size of Nook does not directly translate to easier reading while lying down. The rarely-used keyboard part of Kindle allowed me to hold it between my thumb and palm in one hand, and I had to try many different ways to hold Nook Touch comfortably without touching the screen (which unlike Kindle is touch sensitive). For now, I settled with holding it in its cover folded all the way back, but I am not yet quite satisfied.
Amazon Appstore and from there Kindle for Android. Regular Kindle books are readable without anything else, but Periodical was hard to navigate without "Back" button. For that, I installed SoftKeys, as Nook does not have physical buttons.
I also have ADW Launcher EX (which I already use on my phones) installed. The native Nook application can read B&N Nook books (of course), and I read Google eBooks by downloading them in the Nook format (via the adobe digital editions).
Neither the native Browser application nor Opera Mini seem to give a good browsing experience on this slate, but I am not expecting to use it as a browser anyway, so that is not a huge dissapointment.