Because the Nook uses the epub format it means that all of Google’s books will suit it perfectly.
For the top free books offered by Google go to: free ebooks by Google
If you have a Kindle and want to check out the free ebooks By Google, you still can, but you’ll need to investigate a piece of software called Calibre that will convert the format for you so that you can read it nicely on your Kindle. Follow the link here and I’ve put all the instructions together for you and a link to the free Calibre software 🙂 Have fun!!!