A system for showing which parking spots are available.
Start in a private underground parking garage:
In the middle of every parking spot you put a wireless light sensitive sensor (stick it, make a tiny hole in the ground, whatever). When there's no car on it the sensor detects the artificial lightning, when there is a car on it the light it detects will be a lot less strong. This seems like an easy way to detect whether a car is in that spot or not.
So then you get that information (how much light is detected -> is a car in that spot) on a display showing the free spots. Rather than entering a parking garage with xx free spots and still having to circle around 5 times because you can't find the free ones you can know just see on the display where the free spot is and ride straight to it. That should save you a couple of mins in busy garages. I think people would value that and would be willing to pay slightly more for a garage that has this system in place.
And maybe in the future you don't need a physical display but you could integrate it into people's GPS's or on board computers.
You could also do the same thing outdoors. Will be a bit harder technically (sensor has to be more durable, detecting lightning/whether a car is over the sensor will be harder probably), but if the above works this should work too. When you go to a supermarket at a busy time it can take you a couple of minutes to find a spot just circling the parking. Being able to check the display at the entrance of the parking and drive straight to the free spot seems like it would provide value/make the experience of shopping at that particular supermarket more enjoyable.
Thoughts?
And yeah, I got this idea while spending 15 minutes circling the block for an available spot wondering why I still have to do this in 2012.