Compact fluorescent bulbs. DH recently went on a rampage in our house and we only have one fixture left of standard bulbs in our whole house. For those of you near a BJ's - they have a great deal on a multi pack right now.

Our local power company gave them out for free a few years ago and I stocked up. They came in two sizes and work great inside.

They last for months longer than the regular bulbs and cost about 1/3 less to use.