Flying cars. I read that someone got a patent for one over the summer so that's exciting.
They've been around, in theory, for some time now. Back in about 2004 you could buy a Moller Skycar, if you had half a million or so kicking around idle. It looked sort of like a car with jet engines on it and I have no idea whether it required a driving license, a pilot's license, or both, to operate it.
In some ways I'd love to see flying cars, not least because it would mean you could take direct routes to places rather than having to follow the sometimes tortuous routes the roads take. That said, given the appalling quality of driving I see when people are stuck in two dimensions I shudder to think what would happen if they could go airborne.