I, for one, am a big fan of electric bicycles. You charge them up, you ride them like normal, and if you need a boost, you use it. You could pedal on flat ground and everywhere else and then suddenly you approach a giant hill. You can try to go up the hill if you want, pedaling, or you could use the electricity to get up, aiding you without you even breaking a sweat. I think this sort of thing could be huge if the costs could be a cut a bit. The best part is that there is still that human/manual element to it so people don't have to rely 100% on it.