I have a Sony Pocket reader and love it, the thing is look for the formats you can use on them, a Kindle your pretty much tied to Amazon an pdf. The Lonsome Pine Library system is going to be offering e-books by Christmas they still have to get the system setup, you use your library card to download the book off their website for 2 weeks and then it's gone. I think they will be using epub as one format not sure of what others they will be using havent talked to them about it in a few weeks.

here is a link to wiki that has formats per reader

Comparison of e-book formats - Wikipedia, the free encyclopedia