Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interface
This Kit with fully-dedicated PWM driver chip handles all the motor and speed controls over I2C. Only two data pins (SDA & SCL in addition to the power pins GND & 5V) are required to drive the multiple motors; you can also connect any other I2C devices or shields to the same pins. This makes it drop-in compatible with any Arduino, such as the Uno,...
Arduino Motor Shield Rev3
Arduino Motor Shield Rev3 - Retail
DEV-09815 In Fritzing Library - Ardumoto - Motor Driver Shield
(DRI0009) 2A Motor Shield For Arduino
DEV-10182 - Monster Moto Shield
Pololu Dual MC33926 Motor Driver Shield for Arduino
This shield makes it easy to control two high-power DC motors with your Arduino or Arduino-compatible board. Its twin discrete MOSFET H-bridges support a wide 6.5 V to 30 V operating range and are efficient enough to deliver a continuous 18 A without a heat sink.
Pololu - 2511
This shield makes it easy to control two high-power DC motors with your Arduino or Arduino-compatible board. Its dual robust VNH5019 motor drivers operate from 5.5 to 24 V and can deliver 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. Pololu 2507
The Ardumoto Shield is an easy-to-use dual motor controller for Arduino. Combined with an Arduino, the Ardumoto makes a fantastic controller platform for RC vehicles or even small autonomous robots. KIT-13201