Can I suggest that instead of spending upwards of $65 (that seems to be a
minimum for motor controllers, you build an H-Bridge. They're a simple, intuitive, and fairly cheap (like $5-10) to make. I warn you- you do need some electronics / soldering skills and basic knowledge of circuits and common components.
Here is one decent tutorial:
http://letsmakerobots.com/node/2074
And here is the chip:
http://www.pololu.com/catalog/product/24
And last, here is another method of dual direction motor speed control- the darlington transistor. I very much suggest this method. It's a better place to start. I am making a bunch of these for an animatronic I'm finishing up this summer.
http://bildr.org/2011/03/high-power-...no-and-tip120/
Good Luck!