Product review (5 stars): Great temperature controller for homebrewers.
I wanted to convert an old freezer into a temperature controlled fermentation device.  This controller did the trick at a much lower price than some of the other alternatives that are available.  Another reviewer performed a similar DIY project and posted some great photos of his outcome.  I did something similar using 6 ft lengths of power cables.  The bottom line is that this dual stage controller allows you to plug a freezer into one outlet to lower the temp, and if it gets too cold it will turn off that outlet and switch to a heater plugged into the second outlet.  I'm currently fermenting an ale at a constant 66 degrees.  Get a friend to help you out if you're not the patient type when it comes to wiring this thing up!