This is one of the coolest ideas of come across in a while (and once again I came across it in my most recent issue of Fast Company). Zipcar is a company that is revolutionizing the way people live in urban centers. It can be a fairly expensive and rather unnecessary thing for someone in the city to own a car. Besides paying for parking all the time, you may only need a car for a few hours every week to run various errands - the rest of the time you're riding public transportation or walking. So the basic idea of Zipcar is that scattered around a major metro center (click here to see a map of where they currently are in the US) they have cars parked in reserved parking spaces. As a member of their service you are given a keycard that allows you to walk up to any Zipcar and unlock the doors, activating your reservation. Then you use the car for an hour or two (or as long as you need it), leave it in a parking space, and walk away. The best part? The low hourly rental fee includes gas and insurance, unlike standard car rental agencies.
Check it out - if I lived in an urban center, I would be a member in a heartbeat!