This one would work.
http://www.robotmarketplace.com/products/0-PL755.html
And this one.
http://www.robotshop.com/pololu-high-current-motor-driver.html
Just remember that you will need a way to remove the heat from the hot side when your using the cooler because it will quickly stop being cold as the heat cancels out the affect if it has no wear to go!