Thanks DC42, I also just today found the below, so it looks like the next step is a Mosfet H-bridge !
http://arduino.cc/playground/Main/AdafruitMotorShield
// The L293D motor driver ic doesn't have a good
// brake anyway.
// It uses transistors inside, and not mosfets.
// Some use a software break, by using a short
// reverse voltage.
// This brake will try to brake, by enabling
// the output and by pulling both outputs to ground.
// But it isn't a good break.