This is SparkFun's version of the OpenServo open-source servo controller board. It's meant to replace the existing controller board in any standard servo (~.78 inch servo width).
The Sabertooth 2X12 is one of the most versatile, efficient and easy to use dual motor drivers on the market.
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.