The Nook Color is a great device. but for sheer numbers of free ebooks, Amazon is the winner. (Not that all those books are good).
Oh, and if you run an android operating system on the Nook Color, you can put the Amazon Kindle app on it and get books from both.
What I did was get the refurb NC (cost $119) and then bought the n2a 16 gb SD card ($cost $50). Still cheaper than the Fire. I have the Anddroid Market, plus all of Amazon's free apps go on it. Pretty sweet
I read on my eink Kindles. I send color children's books to the NC.