This year, Smashwords is acting as the hub for the week-long promotion. Participating authors are offing discounts that range from 25% to 100% off the usual purchase price of the book. Smashwords offers all of their titles in a variety of formats for the various e-readers and apps, including Epub, mobi, PDF, text and online versions.
The Smashwords pages also has links to other retailers who are having special promotions for the week, including Apple, Barnes and Noble and the Diesel Book store.
If you are aware of any other retailers and online e-book stores celebrating with sales and discounts, please leave a link in the comments!