A few years back, the 'Copenhagen Wheel' was one of a few innovations in cycling that were being proposed to try to make bicycle commuting easier. While it was just a concept in 2010, it is now a real product, with pre-orders being offered by manufacturer Superpedestrian.
The Copenhagen Wheel is a combination battery and motor that is installed on a Single Speed or 9/10 Speed Free Hub bicycle, converting it into an electric bike with a range of up to 50 km (31 mi) and a top speed of 25 mph (in the US; 25 km/h in the EU). It also provides regenerative braking and Bluetooth connectivity and iOS and Android integration.
For now, Superpedestrian is only selling the Copenhagen Wheel alone, so you'll need to provide your own bike to mount it on. However, the company says that they will soon be selling bikes already equipped with the Copenhagen Wheel. The early-bird pricing for the Copenhagen Wheel is $699 (regular price will be $799 according to the website).
Also previously on EcoGeek: Rubbee Turns Regular Bicycles into Electric Vehicles