Slashdot linked up this detailed, if rather rah-rah, account of the best energy-saver you've never used, the compact flourescent (CF) light bulb. According to the article, Wal Mart is getting into these things in a very big way, and where Wal Mart goes most of America tends to follow.
I bought my first CF in, as I recall, 1992, and paid about $20. Unfortunately it didn't survive my next move, but if it had I think I'd probably still be using it. I was quite shocked the first time I saw a 6-pack at Sams for $12 a few years ago, and they've only gotten cheaper. We've now put them everywhere we can reach where they'll fit and work*, and it's not the savings we noticed. It's the fact that we haven't changed one of them in more than three years that's sold us.
* Two or three of our fixtures use a bulb size which is, as far as I know, unavailable in CF. Those most likely will be replaced soon. Outdoor lights with fancy photosensors won't work with them... something about the voltage I think, not enough to kick-start the bulb. Finally, we have a HUGE fixture in our dining room that holds 7 bulbs. We actually bought 7 CFs for it, but the fixture would only light 3 of them. Again, most likely a voltage thing.