E.T.
We loved the Baby Bjorn Potty Chair. You can buy them at Amazon or Babies R Us or probably other places. It was small enough that my kids could back themselves up to it at age 2 when we started training, and at 4.5, it still functions as the emergency potty in the car. We also bought a potty ring for the regular toilet, but they weren't ready for that until they were a bit bigger, maybe 3.