EcoRenovator has a post on how to make a fridge that runs on 100Wh of energy per day. It's links to a PDF by Tom Chalko* that basically shows you how to modify a chest freezer to operate in temperature ranges.

The nice thing about the fridge is that, when you open the door, the cold air doesn't readily escape, and thus you save energy. The bad things are: you lose a lot of volume of storage, because for the floor space, the fridge is taller than a chest freezer; also, it's a pain to organize and retrieve things from a chest freezer setup, so the ergonomics aren't there.

Still, if your overriding concern is to be good to the environment and to use less energy, this is clearly a relatively easy and effective way to go.

via Make.

*- Boy, is this an interesting side note. Apparently, Dr. Chalko is very keen on the environment, which you will notice from his web site. Also, doing a minimal amount of digging on Google reveals that there is a paper he's written linking an increase in seismic activity to global warming. Apparently, there is no such correlation, but there was quite the kerfuffle about it. All this does not mean that the refrigerator idea is not a sound one.