One of the great things about the app store is that there are so many apps, it forces apps developers to try and promote their app by giving it for free for a limited time.
This is exactly where Free Apps gets into the picture. This cool little app checks the app store every once in a while and updates the list of applications that used to cost money but are now for free!
The UI is not the greatest but comparing to other similar alternatives it works extremely fast and efficient.
Definitely a recommendation by the Mobile Spoon.