Green Motors in Berkeley lent a neighbor of mine a bike to try out with a Golden Motors brushless 500 watt 36 volt rear hub motor. Nice looking set up. I got a chance to try it out, and it has a lot of torque for a fairly inexpensive set up. Top speed was only 18 MPH on a 26 inch wheel bike, so they must have geared them for hill climbing. Acceleration was very good as well. I wonder what it would do at 48 volts! I went up a 20 % grade hill almost as fast as I can with my BMC 900 watt set up.
scroll down and go into the E bike shop. I like that it is an inexpensive set up that is brushless, has good power, is efficient, and is available as a rear wheel set up. They even have a pedelec option and regen available as well.