A 3A, 8-45V bipolar stepper motor driver - this breakout packs a mean punch for it's size! It has built-in overcurrent detection, undervoltage detection, overtemperature detection, stall detection, a 5-bit ADC, and a switch input, microstepping support and PWM drive voltage limiting.
You got some really big motors you want to control? Take a look at the Sabertooth dual 25A motor driver, able to supply 25A each to two motors, at up to 30V. It's a brute, but it's smart enough to talk in many ways!