Chevy Malibu through Hertz on Demand.
Originally I was supposed to get a Fiat 500 but due to some logistic issue, I was reassigned to a Malibu; although still at the same cost as the Fiat (Malibu would have been almost twice as much)
Overall, extremely pleasant experience. The only exception: mother nature (downpour throughout the few hours I had the car for).
If you'd only need a car for a few hours, this program is highly recommended. I like it better than ZipCar because membership is free and car selections are generally better (ar least in my area).