Aerorider

The Aerorider is an interesting machine. A hybrid human- and electric-powered trike, it features a 750W brushless hub motor as well as pedals and gears. Both the Sport and Concept (not yet in production) models weigh around 60kg, so unassisted pedaling would be difficult. However, that's very light compared to most electric cars, so it can cruise at its max speed of 30mph with only a 7kg lithium battery pack.

I've often thought that if motorized vehicles took cues from human-powered ones, we'd have vehicles that used much lighter and simpler components to produce incredible efficiency. The Aerorider seems like an interesting entrant to that category.

A film that shows the Concept in action.

They also make a similar, unassisted version: http://www.sunrider-cycles.com/