The company Sub-Zero has a few fridges with glass doors that allow you to see what's inside. The treehugger aspect of this design is that you can make your menu without letting out the cool air. I don't have any hard numbers, but it's obvious that if hundred of millions of people spent a few minutes less per day with the fridge door open, a significant amount of energy would be saved ("everything counts in large amounts" - bonus points to whoever identifies that quote). Right now, this innovation is only available (to our knowledge) on professional fridges and fairly expensive consumer models, but we can probably expect the feature to trickle down to cheaper models in the near future. Oh, and if you're planning on buying one, don't put it in a sunny corner.