I used a temerature controller like this one
http://www.ebay.com.au/itm/AC-220V-All-purpose-Digital-Temperature-Controller-Sensor-STC-1000-10A-/320822772478?pt=AU_B_I_Electrical_Test_Equipment&hash=item4ab28702fe#ht_4918wt_974
you just have to be careful that it can heat AND cool, not heat OR cool. ie I bought a few controllers before I worked out that they only had a single relay for heating or cooling and you had to select which one you were going to do.

The one that i ended up with, and that ebay listing one, will either activate the heating or cooling circuit at appropriate times.

However, you are reasonably locked in using this method and as such we have been creating the computer controlled version. Have a look at the later blog posts by Greg on this topic, and expect us to have an update in the coming months as to the operation of our fully flexible free control software that allows you to do the exact same thing, and more as the commercial controllers.

The biggest change that I wanted to achieve that I couldn’t with the commercial controller was the ability to have a specific temperature profile that changed over time.
ie start fermentation at 25 degrees, then over 2 days ramp that temp down to 22 degrees, then after 4 days ramp back up to 28 degrees.

That sort of profile will allow you to get the most out of your yeast, and will vary based on what yeast you are using.

This is just a theory of mine that is as yet untested, but it sounds good

cheers

Andrew