UC Press offers a freebie every month, and if you sign up for one, they'll send you a monthly e-mail when a new freebie appears. I use the IOS Bluefire app to read mine, but here's a link in case anyone wants more info for other devices/formats:
http://www.press.uchicago.edu/ebooks/index.html
(That page includes a link to the monthly freebie.)