There is a need for an accurate global (or at least major cities) parking app which shows you free, cheap and safe parking spots. Each parking spot must be able to be reviewed as well: A free parking spot is no good if you are parking in a dodgy area where your car is going to get broken into when it would have cost you a dollar or two for secure parking.
Features to include
Parking type: underground, behind gate, securely manned
Other parking in area
Search by hour/day/month
Data about spot and spots nearby, details about area etc.