Out of all the appliances in a typical home, fridges take the most energy.  They place right after heating/air conditioning in terms of home-energy consumption (it has been estimated that a fridge uses about 15 percent of a home's power).

There are many ways to make the carbon footprint and a hole in your wallet that the fridge leaves, smaller. Every time you open the door, 30% of cool air escapes the fridge and cooling incoming warm air takes a lot of energy than just keeping the items in your fridge cold. So minimize the time the door is open by planning ahead. Instead of browsing with the door open, think what you will take out and where it is, and then go for it, taking multiple items out at a time. Same goes for putting things back into the fridge. To make this easier, it is a good idea to keep the food always in the same area of the fridge - eggs in the bottom (to make them last longest), vegetables in the drawers etc.

When putting food into your fridge, it's a good idea to have food cool on the counter top (as long as it's safe) instead of putting hot food into it. Moist foods should be covered to avoid spending energy that would be wasted on evaporating.

As cooling an empty fridge is a lot more energy-inefficient, it makes sense to keep your fridge full. If you don't have enough groceries to fill it, put your non-perishable food-items in there, too. Also, using gallon-jugs full of water makes your fridge more efficient and less noisy (as it is less on). If your fridge is always half-full it makes sense to get a smaller fridge (try trading it) - it will save you space and money.

Same things apply to your freezer. Full freezer is also useful in case of a blackout - if you don't open the door, the food stays cold in a packed freezer for quite some time.

Other things that might benefit your fridge - keep the coils clean, have some space around the fridge for the warm air to escape, make sure the seals on the door are tight and that the fridge is not right next to the stove. Defrosting the fridge regularly and turning it off altogether when leaving for a vacation are also good ideas to not waste energy. The best temperatures for your fridge are 37 to 40 degrees Fahrenheit int he cooling section and under 5 degrees in the freezer compartment.

When buying a new fridge, it's a good idea to get one that's Energy Star qualified. They use less energy, thus polluting the planet less and saving money for you.