EBay temp controller, hands down.
Two stage let's you control both a heater and cooler at the same time.
Print out a Fahrenheit to Celsius conversion chart and you're set.
Total cost: less than $40.
I'm currently using 2. Have held 35 for 2 weeks so far on one side of my ferm chamber.
Conditioning: Muddy Paw Nut Brown Ale, Jump The Fence Independence Cream Ale