Welcome to MR, Lianne, and congratulations on your new Nook!
It looks like you have discovered some great places to get books. Have you checked our Wiki? There is a page devoted to
free book sites. Plus, just in case you haven't found them:
smashwords.com and
baen.com which has a
great free library.
Then, of course, the MR Library with thousands of book beautifully formatted by some very dedicated MR members.
ePub format
Have fun continuing to explore MR and just ask if you have any questions.