We bought the Nook for my daughter for her birthday. She loves it because she always has her nose in a book. I liked the fact that you can put microsd cards in them to expand the memory, or to keep all of a certain genre together.
Which ever one you get, there are lots of great sites for downloading free e-books:
Project Gutenberg:
Project Gutenberg - free ebooks online download for iPad, Kindle, Nook, Android, iPhone, iPod Touch, Sony Reader
Google books:
Google Books
Internet Archive:
Free Books : Download & Streaming : Ebook and Texts Archive : Internet Archive
Also, lots of libraries are offering ePub books now, so you can "borrow" an ebook from them.
My husband has been trying to talk me in to getting one, but I'm old school. I like the feel of the paper in hands. Plus, the tub is my favorite place to read... so that rules out anything electronic for me.