One of my earlier books (on which I worked with a number of other writers), HarnMaster Barbarians, has recently been released as a PDF on DriveThruRPG. The original was a loose-leaf product, not a bound book, so, with some decent quality paper, the PDF really isn't that different from the original hardcopy - and it's cheaper, too.
I have updated the Writing Credits page of my website with the direct link to the purchase site, and with similar details for any other books I've contributed to that remain available.
