• Make sure your weatherstripping is up to date around your windows. Here's a very thorough How-To on the weather channel site. Find out about caulking gaps between doors and windows on the Lowe's Site.
• If your windows are very, very drafty, like they're single paned and old and don't quite fit in their frames anymore, it's not pretty but consider some sheeting to keep the cold from moving inside.
• Likewise Drawing the drapes can keep a lot of cold out (it also helps to keep heat out in the summer, bonus!) especially if you change to thicker drapes in the winter. Here's a good question about Hanging Wall to Wall Curtains.
• On hard wood floors add some rugs (wool is warmest) and to keep more heat inside to keep your feet from freezing (wear socks too)!
• Get Rich Slowly has some great tips for staying warm in the winter including bundling up and setting your thermostat to the optimum temperature.
• If you have a fireplace, make sure you have a damper and a screen to keep all the heat from escaping up the chimney.
• And if your house just gets cold (we've been known to be frugal enough to refuse to turn the heat on until the 1st of the year) check out a round up of How To Stay Cozy Inside.
Here are some other roundups:
Roundup: House Tour Coffee Tables
Roundup: Best Staircase Storage
Roundup: Best Travel Alarm Clocks
Roundup: Traditional Ikea Elements
Roundup: See Through Furniture
Roundup: Landing Strips
Roundup: 6 Side Table options