I did this over the weekend: I hauled my very very old upright freezer to the basement, where the temp is pretty steady around 58-62.
I wired up a $12 120v line thermostat (like what you'd use for baseboard heat) and a porcelain light fixture w/ a 15 watt bulb.
It works fine: the thermostat isn't calibrated very accurately, but after some trial and error I have it holding steady at about 68 right now. I've going to be brewing some Belgians soon: this will really help hold that temp a little higher (I might shoot for more like 74 for the saison--I might need a higher watt bulb to hold that temp.)
The bulb fits perfectly in the chiller compartment of the old freezer so that the beer is protected from the light.
Bottle conditioning: Robust Porter
Drinking: Saison Dupont clone, tripel
Coming soon: Columbus APA, Rich Red ale