Packt Publishing is offering $5 (USD) e-books when two or more are purchased through 3 January 2013. Their Stock Your Reader for Christmas page contains the details and I have included a snapshot of that here.
I've had my eye on a few of Packt's books, but wasn't sure how much time I'd have to read them. However, at $5 a piece, it was an easy decision to purchase them, even if I'm only able to browse them and read the most interesting portions. To take advantage of the deal, two of more e-books must be purchased. Fortunately, all of the Packt Publishing books appear to be part of this deal rather than a limited selection. As the next two screen snapshots indicate, I was able to purchase six e-books of interest to me for $30 (USD).
I don't know how good each of these books is, but at $5 per book, it wasn't much of a gamble. As the screen snapshots above indicate, I ended up purchasing Play Framework Cookbook (August 2011), HTML5 Mobile Development Cookbook (February 2012), PhoneGap Beginner's Guide (September 2011), EJB 3.1 Cookbook (June 2011), Apache Maven 3 Cookbook (August 2011), and Java EE 6 with GlassFish 3 Application Server (July 2010). I am tempted to go back and purchase the PhoneGap Mobile Application Development Cookbook (October 2012) e-book and, because you need at least two for the $5 each deal, I may be "forced" to purchase HTML5 Canvas Cookbook (November 2011) as well. For the typical price of a single book, I am able to get 6 to 8 books in a variety of subjects with this offer.