Inkbird's awesome temperature controller is part of the current eBay 20% sale and they haven't jacked prices, plus delivery is included. w00t!
I've got one of these and use it for homebrew, and it's simply awesome. Use it to control a fridge or freezer and keep the temperature at a nice, steady, even level to produce superior results. It's the single best upgrade to my homebrew kit that I ever did. Apparently it's good for aquariums and terrariums as well.
There are a few versions of this controller that will suit various needs:
ITC-308 with basic probe - $39.59/$38.60 w/ Plus
ITC-308 with removable probe - $39.99/$38.99 w/ Plus
ITC-308 with removeable 12" steel probe $43.99/$42.89 w/ Plus
Wireless ITC-308 with basic probe $47.99/$46.79 w/ Plus
These are great. Ive used one to convert a slow cooker into a yogurt maker.