For those interested in the topic, click here to obtain a free download of Policy and Choice: Public Finance through the Lens of Behavioral Economics by William J. Congdon, Jeffrey R. Kling, and Sendhil Mullainathan.
To be clear, this download is not a pirated copy but a free electronic version authorized by the authors. I don't expect this kind of thing to be the beginning of a trend. A free-download strategy makes sense when an author's sole goal is maximizing readership and intellectual influence. Most authors, however, from novelists to (of course) textbook writers, have some pecuniary motives as well.