Bonus Extra Instructables:
For less than $70 you can also build your own "PID" controller from an arduino with this instructable. An aquarium heater works well in a cooler to keep a constant temperature. Here is how to rig it to be always on. With those two projects you can have a "set and forgot" system that is accurate to 1 degree F.
This instructable is unique in the use of the hacked aquarium thermometer to heat the water when it starts to cool. It allows much more precise control than a tea pot heating method. If you don't want to hack a heater, I describe how to heat water on the stove. It's just more labor intensive. This method is still under manual control, but you just plug and unplug the heater. If you add the PID controller, it's all automatic.
Sous-Vide means "under vacuum". As a cooking method, it's a key to perfectly cooked meats that don't need babysitting or split second timing. It's even possible cook eggs and custards to perfection. This instructable will show you how you can experiment with this technique using equipment that is much cheaper. if you already have a water tight beer cooler and a vaccuum sealer of some kind, you might even already have everything you need. Douglas Baldwin's web page has a lot of information and recipes once you have the basics sorted out. Also check out EWilhelm's Sousvide instructable, which is partially what got us started. Eric uses a commercial temperature controller which allows more hands-off cooking, but increases the cost about double what our Aruino based solution did. If you want to try this cooking method out on the cheap, read through here and you can probably do your first meal with what you have laying around. Beware, you may get hooked on perfect steak and end up spending your weekends soldering up controllers for friends and family.