Embraer also designed what later became the ERJ145 with engines atop the wings but it seems that configuration isn't quite nice aerodynamically as the underslung version. Maybe something to do with clean flow over the top being more important than round the bottom.
Imagine how "unreachable" engines atop a high-wing plane would be for maintenance (also for FOD as well :-)
There were some experiments by Boeing and Antonov with engines on top and engine flow attached to the wing and over the flaps for better low-speed lift but that seems to be a specialty application and the exhaust gases cause corrosion on the structures exposed to them.
It seems a few years from now every new airplane will look like a 737/320. Even the new "big" regional airlines (Dornier/Embraer) have this layout and only those too small to make a higher gear viable keep the engines in the back.....