These dual VNH3SP30 motor driver carriers are perfect for driving two high-power motors through one compact unit. With these boards, it's easy to get a medium-sized, differential drive robot running in no time. The VNH3 version is a lower-cost option than its VNH2 counterpart.
Pololu is known for some killer motor driver technology. They're bringing their mojo to the Arduino! Dual robust VNH5019 motor drivers take 5.5 to 24 V and punch out a continuous 12 A (30 A peak) per motor, or a continuous 24 A (60 A peak) to a single motor connected to both channels.
Here is a motor controller that only needs 2 lines for control, it communicates serially via 2400 or 9600 Baud TTL signals. It's a smart controller that has a number of parameters that can be adjusted and can return valuable data such as speed & position.
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.