Congrats on getting a wonderful gift! I got a sony 505 for my birthday this past November. It was a wonderful gift! I'm sure you'll enjoy yours as well.
I'm a total cheapskate. I download books from this site, from feedbooks.com, and, mostly, from my local library. Check out this site to do a search on your library to see if you have ebooks available:
http://search.overdrive.com/
There is also
a link to digital library collections and information about obtaining cards in the 500/505 forum.
welcome to the forum!