Details can be found here:
http://www.tor.com/blogs/2011/11/wild-cards-ebooks-now-299
If you're an ebook reader who has yet to sample the Wild Cards series, here's your chance to get a taste. I'd recommend that you start with either WILD CARDS (where it all began) or with INSIDE STRAIGHT (first of the "next generation" books, and a great intro to the world). But hell, at that price, you can buy all four for less than the price of a pizza.