Thanks to Astaryth (Jeanie) for giving me a heads-up on Nook originally, and for sharing the information about the libraries. Even our lowly little hick-town library has joined the modern world!
Kindle is the cheapest, but it is not on the library's list of compatible readers. Books can be downloaded to a PC or Mac, but I spend far too much time in this chair now; I certainly don't need to be sitting here to read a book. Besides, I'd be distracted all the time: I'd be reading a chapter and think, "I need to check my email" or "Oh, my potatoes are ready to harvest in Farmville."
Now all I have to do is wait until the price of the Nook drops for Christmas. If I'm able.
The Ipad was never in the running. It's just too pricey, and I have no need for a multi-purpose device.