Upgrade your stock brushed motor with the new Sport Tuned range modifieds from Etronix. These motors boast some great features for their price point such as rebuildable can and endbell design, ball bearings and replaceable brushes and springs.
While the quality of components is good for the price, factory assembly seems a bit hit and miss. Endbell and can sticker orientation appear to be quite random, which means that connecting the positive wire to the motor's "+" terminal will not necessarily make the motor rotate in the direction indicated by the arrow on the can, which in turn is not necessarily standard forward rotation. However the motor is rebuilable, so it isn't hard to strip it and reassemble everything the right way around.