I'd highly recommend the Hampton Bay (Home Depot) fans with the "quick connect" style blades. (I'm not sure exactly what it is called, but it is specifically mentioned on the box as being easy to assemble)
Anyway, they weren't lying. I've put up probably 10-12 fans in my life and this last set that I got for my house were by FAR the easiest. Everything on the fan basically snapped into place (blades, light fixtures, trim pieces, etc) and it was just a matter of hanging the mount and hooking up the wires. Took like 10-15 mins per fan after I did the first one.
Compare this to some of my previous fan adventures, which involved screwing everything together (3 screws per blade), balancing the blades, running wires through the fan for the light kit, hooking up the light kit, securing the light trim etc, which took about 45-60 mins per fan.
I was surprised. I bought them because they were relatively cheap ($60? $80?) and didn't think I'd be too impressed, but overall I have been very happy with them. They won't save you any time in actually putting the fan box into the ceiling, but at least you can reduce the hassle of "fan assembly."