Most Creative Commons works available are SF.
Right now I'm reading
Postsingular from Rudy Rucker, but popular books like
Accelerando from Charles Stross and
Down and Out in the Magic Kingdom from Cory Doctorow are excellent too.
CC Science-Fiction:
http://www.feedbooks.com/list/view/22
CC Fantasy:
http://www.feedbooks.com/list/view/25
First book that I actually read on my Sony PRS-500 was
Oblomov from Goncharov. I love russian literature, but I've already finished reading most of the classics. This was a perfect choice for me.