My home airport (MCI) has a parking program for its own lots. Pretty good system: they send you a card which you use to get in and out of the lots, and you earn points for free parking days later. Best part is everything is online: both receipts for the paid days as well as a simple interface to tag your upcoming days as award days. My regular business travel earns enough points to cover all of our leisure trips.

There's also the Parking Spot nearby with its own program. But the airport program is better since I can earn on close-in parking for business trips and redeem on long-term parking a similar distance away as the Parking Spot.