Two books, by Isaac Asimov, and Robert Heinlein, in Kindle format, available for .35 now on Amazon.
http://www.amazon.com/Double-Star/dp...011288&sr=1-99
http://www.amazon.com/I-Robot/dp/B00...11288&sr=1-100
Posting this before I double check to see if they aren't available somewhere else for free.........