You may not think that think that this tip will save you that much money, but it could possibly save you in key replacement and/or having a professional come out to get you into your house. Here's a great trick from homedit to help you never forget your keys again:
Simply remove the switch plate and place a small neodymium magnet in the light switch. Replace the plate and voila it's magnetized! In the image above you can see that they placed the magnet inside the switch but you could also tape the magnet to the back of the switch plate.