This is the first in an on-going series on how to make your life better and save the planet all at once. I'm going to start with the simplest and easiest things and move on to the harder things later.
So in that philosophy, there's not much simpler in life than changing your light bulbs. I first discovered complex light bulbs way back in 1991 when a basic CF light bulb was around $10-15. But even with that, by just changing the bulbs in the lights that I used the most, I saw a significant drop in my electric bills. Now that you can buy bulbs at the dollar store, it's an even better deal. Taking a look at light bulbs at Ralph's recently, I found that while the unit cost of a CFL bulb was higher than that of a traditional light bulb, since they last longer, the actual cost in bulbs was exactly the same. Then you throw in the savings in electric bills and you're actually coming out ahead in your bills.
So get yourself out to the store and change some bulbs. Start with the lights that you use the most, and then move on from there.
There are some negatives to watch out for though: Some light fixtures (rather rare) can reduce the life span of your bulbs. Also, there is a small amount of mercury in each bulb. IKEA and many other stores that sell CFL bulbs will take the dead bulbs back for recycling at no charge. Note that they must be unbroken to do so. If you do break a bulb accidentally, the amount of mercury is small enough that you don't need to get a biohazard suit on, but it's better not to pile these up in our landfills without first removing the mercury.
More information: CFL article at wikipedia
CFL FAQ from GE
Buy compact fluorescents from amazon (IKEA is cheaper though)
NP: "What's a Planet? - SciFri Podcast - 2006081824," Science Friday Podcast.
WC: 11918, ECD: 30 April 2007.