Calibre is great software. I would highly recommend installing it(
http://calibre.kovidgoyal.net/download).
If you like older books, there are many free public domain books floating around the internet. Try manybooks.net, feedbooks.com and munseys.com to start. They are all searchable by title, author and genre.
For newer books look around for DRM free ebooks whenever possible.
Calibre can convert almost any ebook format into lrf or epub which is compatible with your reader. So as long as it's DRM-free it will work. It will also download the New York Times or Washington Post among other news sources to your reader every day.