From my experience of working with electric bike projects at our shop, if anyone knows how to build a fast, efficient bicycle that can take a beating it's the companies who have teamed up on that project. For some more personal examples of electric bike posts visit this page at The Hub Blogs.
This raises the question "is this the direction bicycles are taking for meeting demands of everyday bicycle commuters?" Electric and pedal driven bikes that remind me of the old Honda gas powered mopeds?
Several years ago we built up an electric tricycle with extra batteries and had that thing humming along at 40 mph with a kit from Wilderness Energy. (Reviews of that kit at amazon aren't very good and I haven't seen the hub motor kit available with disc brake). Later the new owner of that bike was going to try rigging up some solar kit for riding across New Mexico. Haven't heard from him since but knowing we had some success with the project and after reading the article mentioned previously and seeing the photo at right has got me recollecting the challenges of building something stout enough to handle the speed, braking and bumps that routinely going 25 to 30 mph does to a bike.
Bicycling Magazine has an excellent article of Four e bikes they tested and reviewed. A retailer of some of those bikes reviewed are at NYCE Wheels. At their site they also have high quality electric motor kits and lots of information for researching an electric bike purchase. So far the kits and bikes from Currie Technologies is getting good reviews and there is a kit from OEM that comes with a rear wheel and disc brake. Here is a bit of advice I received from a reviewer.
Don't EVER buy any e-bike unless it runs at 48 volts or HIGHER ! The higher voltage gives you so many benefits. I have tested over 35 different e-bikes and everything under 48 volts has been bad. Almost EVERY e-bike that had 48--52 volts motor and running over 500 watts was GOOD. Max. watts output should be above 1000 watts to get a 220 pound rider up any 20---25% uphill. ALSO, The Lithium batteries (any of them) made in USA or Germany are sooooo much better. Recently the USA and Germany is getting very competitive with Chinese prices and USA has better quality and warranty.
Perhaps the most well reviewed e bike I found and is available as a folding bike as well.