Celebrating a gajillion app sales, and for an unknown length of time, there are dozens of free iPad and iPhone apps available.

The original 10 are at: AppShopper » Apple Celebrates App Store’s Fifth Year with 10 Free Apps

Subsequently, many more have been released, and are mixed into AppShopper’s usual fare:

iPad Apps, iPhone Apps, Deals and Discovery at App Shopper – Popular Recent Changes for iOS