Now through September 5 at 12:00pm Pacific, you can download inFamous: Second Son on PlayStation Network for $39.59. Not the steepest price cut, especially for a "flash sale," but 20 bucks is 20 bucks. Worth considering if you aren't opposed to owning games digitally.
Easily one of the best titles on PS4. And it's got a photo mode, too.
inFAMOUS Second Son Flash Sale Starts Now [PlayStation Blog]