An automobile powered by electricity. For some time (and still) development was thought to be waiting on drastic improvements in battery technology--cost, weight, charge/discharge rates, and longevity are all factors. It's thought that ultracapacitor technology may help with the situation. My bet's on hybrid-electric vehicles.

My father had an electric car when I was a child. I don't remember the brand, but it was based on an AMC body. The heating system was based on the recirculation of transmission fluid. In retrospect, this implies to me that the design didn't leverage many of the purported advantages of an electric motor--i.e.: an electric car shouldn't require a transmission. Anyway, I distinctly remember the time that some hose came loose and the thing bled a bunch of bright red transmission fluid all over the driveway.

I suppose if they were clever (which they werent), they might have gone with heated seats instead of an arcanely complex use of heat-exchangers and recirculated transmission fluid. Or maybe electric cars aren't meant for cold climates like Detroit.