Since I can't afford to replace my windows like Andrea did recently (I've got a lot more of them for one thing), the next best thing is to be sure the existing ones-- which are double-paned, so that's a help—are well sealed.
One of my energy audit recommendations was to caulk the window frames inside and out. My handyman friend Rob and his brother got the outside of the windows caulked (hmm, I have to ask him about the basement windows -- it's kind of tucked away under the entry deck over the dog door.) He said that it looked like some of the edges (the tops of the second floor windows especially) hadn't ever been done and the ones that had, had highly degraded foam insulation, squirted in probably 30+ years ago when the house was built. He removed the old foam and sealed the edges with new caulk. Now it's time to do my part, sealing the inside of each window. (I'm already falling behind on my "window a week" plan. Oh well.)
Next step: check the doors. I've got three exterior doors, a slider that opens directly to the outside, and one door that opens into the unheated (but insulated) garage. The old weather stripping is starting to peel off in places, and I've started replacing it on a couple of the doors. I got the door to the garage done last winter. However, the past few months my old dog liked to lie in front of that door -- perhaps it's got cooler air from the garage coming in beneath the door, so I guess I need to get a sweep or something for the bottom, which I didn't think about then. You take your information where you find it!
In addition to the weather stripping, the windows in the exterior doors themselves should probably be caulked and/or replaced -- the doors are in good shape, and apparently you can buy new insets to replace the windows in the doors. The two storm doors need to be replaced -- they almost blew off their hinges in some of the really bad spring wind storms. That's getting more imperative by the week, so that will be the next project for Rob. However, every time I think I know what type I want, something comes up to make me take another look -- Do I want just a plain storm door? Or something that's somewhat or ultra energy efficient? Or a security storm door? There have been a couple break-ins recently in my usually very safe neighborhood. Or…??? I guess I'd better make up my mind soon!