[meyer]

Something else you can do is go to Lowes or Home Depot and get a can of Great Stuff for about $5-$6 and go around to all your outside walls, remove the electric wall plates and seal around the electrical boxes.

Great Stuff is great stuff, but be careful - it REALLY expands! I put some in a wall cavity when I was putting a shop room in the garage. I sprayed it into the crack in the corner cavity (used fiberglass in the rest of the wall but this crevice was too small to get into) and then went upstairs. When I checked on it a few hours later, I had a big 6" round, 8 foot tall blob of expanded foam sticking out of a 1/2 inch crevice! Had to let it dry completely before I cut it away with a razor.

[plinyelder]

I bought some of those foam-like insulators that you just take the faceplate off the wall and put those behind them.