Kits like the eZee are nice because if you run out of electricity peddling around a 7-10lb motor is no big deal compared to a larger direct drive. My 9c hub is a bear to chug around on no electricity.
I have a ebikekit.com kit and the gears eventually wore down and gave out. I thought it would be cheap and easy to replace gears, but it turns out it's just cheaper to buy a whole new hub. I don't think I will ever buy a geared motor again.
Big direct drive hub motors can go on seemingly forever with occasional bearing changes and are preferable to smaller hubs because what always ends up happening is you go out thinking you are only going to use the thing thing to help on the hills, only use it when you get tired, ect... and it is just too fun not to use them like a segway or something. Little direct drive motors get hot too quick to be used like that.
Here's my breakdown of what kit I think you should get (not including battery) and why:
best deal: 9C kit from ebike.ca: $505 because you get the super handy, and widely used cycle analyst, which is essential to avoid overdischarging and managing efficiency. Well known for reliability, and lighter than Crystalite 45xxx series. You get a reliable but pitifully limited 20amp infineon controller with your kit.
2nd best deal: Magic Pie v3 from goldenmotor.ca: $392: known for being able to handle abuse of extreme overvolt/overamp loads. Effective, useful integrated cooling fan system. Sub-par 35a speed controllers built right in the questionable location of right in your hub, heavier 20lb motor.
3rd best deal: Max's Crystalite deal at ebikedeal.com $470-550: you get the knock off of the cycle analyst called "APM" the less preferable, but still darn good 16lb cyrtalite ht3525 and a killer awesome controller. Great kit for the price, but I almost want to give the 9c the edge over ht3525 for some reason.
4th best deal: That Yescom 1000w 48v motor that goes by a bunch of different names and sells for about $280:http://www.ebay.com/itm/48V1000W-26-Rea ... 552wt_1344http://www.amazon.com/1000w-Wheel-Elect ... 005&sr=8-9
Clone of the goldenmotor prokit 901. Great amount of bang for the buck. Can't handle overvolting very well, lame-sauce 20a controller, cheapie plastic throttle. Good reviews, one of the better e-bay kits out there.
Hope this helps