power/heat bills
I know you've all heard and done this before, that is spraying expanding foam into cracks. But, if you have a crawl space, or an attic, go into those areas after dark, first turning on ALL the lights inside the house. You'll be surprised at how much light you'll be able to see. When you inspect an area for light, after your first look, go a few feet and turn around and look again, often you'll see light that you couldn't see before. Fill those spots with expanding foam.
When using the expanding foam spray can in the crawl space you'll need a small diameter hose to put over the supplied straw from the can. That way you'll be better able to get to the small holes and cracks that are in very awkward to get to places.
Hope this helps you. dgh