Gizmag have an article on a car which Tata is going to produce which runs on compressed air.  This means the only impact on the environment is the energy used to actually compress the air.  The exhaust fumes are just cool, unpolluted air!

The company says that the car will cost about R30 to fill up at air pumps at upgraded petrol stations.  It will then be able to travel 200 to 300 km with a max speed of about 110 km/h.

If this actually works it will be great for cities.  Almost no pollution and cheap to run.