Serendipity! I get annoyed by a Fox News guest ignorantly citing Kurt Vonnegut to buttress his politics back in June, but wait until September to get around to writing a post about it, in which I note my appreciation of Vonnegut's books, then a day later I see that Amazon Kindle is offering 18 of his books through September 28 for four dollars.
I have read fifteen of his works and have enjoyed every one of those reads, but if you have not read any of his works before, I would have to say that Slaughterhouse Five* (his most important/famous novel), Breakfast of Champions, and maybe Cat's Cradle are the ones I would start with.
There's also the recently launched Kindle Daily Deal which is fairly self-explanatory: it features a different book from a different genre everday at a discounted price ranging from a dollar to three or four dollars.
And, finally, thanks to the tip from Sheldon, there is Dean Baker's The End of Loser Liberalism: Making Markets Progressive for a dollar which can also be found for free in pdf format. Baker describes the book, here.
*I must note that Vonnegut unfortunately relied on the figures of Holocaust denier David Irving to inflate the number of dead in Dresden from Allied firebombing - a central event in the novel - from around 25,000 to 140,000. Although it is unlikely that Vonnegut would have realized what Irving's true intentions were, even after it came to light (thanks largely to the work of Deborah Lipstadt) that Irving was an anti-Semitic liar, Vonneut for whatever reason stuck to the original false figures in his book.