I just got this:
http://www.amazon.com/A2B-Lithium-El.../dp/B0021IQP8A
(without the extra battery)
This is the most motorcycle-like bicycling experience I've ever had. Biggish tires turn in by countersteering, it falls nicely into corners at 20 mph, and I am not afraid of having to crawl up Seattle hills at 3 mph anymore. It is harder to pedal than a lightweight bike, but the electric assist more than compensates for it.