In Electric Bikes, Go Green, Not Mean - Drawing The Line I noted someone discussing the need for a transmission on electric motorcycles. I think the same is true for electric bicycles. At Interbike I had a chance to try the NuVinci CVT and am very impressed.
It was on a bicycle but if you look around their website (http://www.fallbrooktech.com/) it's clear they are targeting other vehicles in addition to bicycles. On the bicycle there was a selector lever on the handlebar, and you chould change the ratio at any time you like. Unlike on a derailleur bicycle where the wheels have to be moving to change the ratio, with the NuVinci CVT the ratio can be changed whenever you want.
The ratio is determined by the positioning of some balls inside the CVT. It looks really cool.
I have a flyer from them in my hand saying the NuVinci is available in a ready-to-install aftermarket kit or pre-laced in a rear wheel. Unfortunately their website doesn't have a product description, but there are some press releases that discuss this
The press kit has a lot of information and a history of the company. An interesting thing is that they have a sister company who's using the NuVinci CVT in a small scale wind turbine.