If you like science fiction and/or fantasy, Baen Books has been offering e-books direct to the public for many years now. And one of the formats they offer is specifically for the Sony e-book readers. Baen has a free library and also a webscriptions program that offeres a bundle of books every month for about what one hardback costs. Overall they have a very forward-thinking e-book strategy. The web address is
http://www.baen.com/.
And please remember that some of the things that are categorized as "science fiction" or "fantasy" might surprise you.
