We got one of these for our robotics project:Pololu Dual MC33887 Motor Driver Carrier
It will go up to nearly 30V, and can handle up to 5A per motor. Very easy to control as well, though the pin layout looks complicated. All you absolutely have to hook up for it to work is the Enable, Disable2', IN1, and IN2 on each motor, along with a ground (so for minimum operation of two motors you need 8 signal pins and one ground pin on your microcontroller). All you do is bring the Enable and NOT-Disable pins high, and then control the direction of the motor by bringing one of the IN pins high and the other low. Easy as cake. You can also do fairly precise speed control using PWM either in hardware or software.
If you want to get really fancy you can also use the feedback pins for more precise control loops to help you regulate power to your motors. We aren't using this personally, but I can see how it might be useful in some applications. If you like it and want more info about it, just PM me or ask here and I'll try and answer any questions you might have. (And no, I'm not a corporate hack, I actually found the recommendation for this controller on another thread in this very forum and have simply grown quite fond of it.)