Surfing the Kindle store this afternoon I came across Karel Capek's War with the Newts (1936) - a sci-fi satire about a global war between humanity and an intelligent race of newts - for $1.05. (You can read the book online for free, here.)
Although I consider myself a book geek, I must confess that I had never heard of this book, despite being vaguely aware that Capek is credited with popularizing the term "robot" in his earlier work R.U.R. (1920) which can also be found for 1.05 on the Kindle (and Dover offers a $2.50 pb edition). I should have heard of it, however, given that Robert Zubrin, author of The Holy Land, one of the books on my list of books I've wanted to read but haven't yet, cites War with the Newts as an inspiration.
Unrelated to sci-fi, but another interesting book (play, actually) I came across for the Kindle is Socrates by Voltaire for $0.99 (It can be read on-line, here, if you scroll down.) I don't know much about it other than that a play about Socrates by one of the great satirists and leaders of the Enlightenment (I would expect Voltaire to use the trial of Socrates as an allegory) is something I'm excited to read.