Flip em off.

You leave the bathroom, leave the light on for two hours. You leave the living room for 45 minutes, TV is blaring in the background. These things are all costing you money every month. Remind yourself and your family to shut off the light or TV when exiting a room.

Another way to save money/energy is to check all your door seals for leakage. If they look dry rotted, torn, or can see light through it, it's time to replace it.

As far as your air conditioner goes, it will actually save money to leave it on a reasonable temperature during the summer months when it will be operated a lot anyway. This is because it takes quite a bit of energy to repeatedly get the house to your set temp, instead of just keeping it at or near that temp. It's kind of like how semi trucks keep there engines running at truck stops.

You can check out some itemized monthly energy costs here:
http://www.energycheckup.com/content/EnergyDollars.asp

All of this stuff can save you money every month, as well as help the environment. I am not going to monetize this one because I already do these things, instead I just wanted to share it with new home owners.