Welcome to MR, Chocomoholic
I've had the Sony 505 for a year and love it.
Your Sony can use ePub and lrf from this site. Have you seen all the free ebooks here? Look up on the left on the blue bar. Any ePub or lrf will work on the Sony.
We also have many author members who put their books up for free or a small purchase price. Check out my signature for just a few (especially the feedbooks list).
You can also follow the Writers' Corner and the Deals, Freebies, and Resources thread for other information.