There are several ways to reduce on-power understeer, as other RCTechies have mentioned. I'll address one that is not usually given: lowering the center of gravity (CG) as much as possible. Keep the ride height as low permissible, and the radio components and wiring as low possible. Another possibility, depending on the car, is to lengthen the wheelbase. I have had good luck running my XTi in the long/long (chassis/motor pod) configuration, which reduces weight transfer under acceleration just like a lower CG does.

The nice thing about lowering the CG and/or lengthening the wheelbase is that it also makes the car less "pointy" on turn-in, which is great for those of us whose reflexes have slowed over the years.