I published a short book last year using blurb.com. The service was easy to use and helped a publishing neophyte like myself produce a relatively professional looking book. To accompany the book I allowed a 15 page preview to be available. There was a lot of interest in the book but nobody bought a copy. So I figured I might as well put the whole book online for free. That's when folks started buying copies!
I think it's interesting that completely free content lead to my first real sales, and now I've received my first royalty cheque. Of course, after tax, that cheque is barely enough to buy myself & a friend a couple of coffees at Starbucks. But I'm proud of it!
P.S. Here's the free link: http://www.blurb.com/books/960910