And the winner is...
As you can see on the chart, fanning your car by opening and closing your door a few times with the passenger-side window down is still a faster way to cool off the car for the first few minutes. It actually wins the degrees-per-minute battle by a score of 3.6 to 3.1, whereas the control is 1.8 over that time frame and driving the first two minutes with the windows down is 2.5 degrees per minute.
The biggest takeaway: keep driving
If you know anything about air-conditioning systems, you know that they require an immense amount of wind passing over the condenser (the radiator-like object that's usually next to the, um, radiator) in order to effectively transfer enough heat. This is why many cars have a dedicated auxiliary fan that can help out if you're not moving fast enough. However, the system isn't optimized to run while you're stopped for long periods of time, as evidenced by the graph -- not to mention it's by far the worst option for your car's long-term health. Whereas the control test is clearly the outlier of the group, the other three tests all generally coalesce around a point of diminishing returns.