Maybe the best idea for the car of the future: the air compressor powered car. Last year I saw that a French designer had come up with this technology–after reading about the company making these cars, it appears he is involved with the design for these as well.
The basic idea is this: they inject compressed air into the cylinders of the motor, pushing the pistons at the right times, which just like in internal combustion motors, turns a crankshaft, thus turning the wheels. Interesting idea, since the only waste material is not so compressed air. Great idea! And the technology has improved quite a bit from the show I saw about them last year.