The PhidgetAdvancedServo 1-Motor allows you to control the position, velocity, and acceleration of one RC servo motor.
The PhidgetStepper Unipolar allows you to control the position, velocity, and acceleration of up to 4 unipolar stepper motors.
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.
SparkFun's collaborative effort with Brian Schmalz makes the EasyDriver stepper motor driver compatible with anything that can output a digital 0 to 5V pulse.
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.
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!
The Sabertooth 2X12 is one of the most versatile, efficient and easy to use dual motor drivers on the market.