You've probably heard about Solid State Lighting; Light Emitting Diodes (LEDs). You may already know that you can buy inexpensive LED flashlights which have very long run-times (got $10 to spare? How about $5?).
What you may not know is that 2006 marked a major turning point in LED technology; The light output, power efficiency, and price of these chips which emit light improved drastically, and just as Moore's Law "governed" a relentless march toward faster, cheaper computer chips, Haitz's Law predicts LED technology will get better and cheaper at a rapid pace.
The products making LED lighting a good choice for general illumination in your home are not yet available. Even if you're an "early adopter" willing to pay extra for the "cool factor" like I am, the products just aren't there yet. When the first products shining around 600 lumens, like this one, hit about $45, I'll buy one (good luck finding one available right now, and if you do, it'll probably cost $100 or more).
Are you're accustomed to measuring lighting products by their "wattage"? If so, break that bad habit immediately. The standard measure of light output is the "lumen."
An ordinary "60 watt" incandescent bulb produces about 850 lumens; That means you get about 14.2 lumens per watt of energy consumed. By comparison, compact fluorescent bulbs are about 4 times more efficient; In other words, you can get around 850 lumens, but consume only around 15 watts, for energy efficiency of around 60 lumens per watt.
LED technology didn't stack up very well; Until 2006.
6/20/2006: Cree Demonstrates 131 Lumens per Watt White LED
8/9/2006:: Cree Delivers the First 160-Lumen White Power LED
12/5/2006: Seoul Semiconductor Introduces the World's Brightest LED, A 240 Lumens Single Die Light Source
Current LED products can now produce over 100 lumens per watt, substantially better than compact fluorescents.
You can expect LED chips to continue getting brighter, more efficient, and no less importantly, cheaper. You can order a single Cree XLamp for $7.25, shipped, but unless you enjoy soldering, I wouldn't recommend doing so.
So, what's the bottom line? Replace any incandescents you've still got (unless they're on a dimmer or motion sensor) with compact fluorescents. Don't even think about buying an incandescent flashlight. And sit tight for the explosion of general purpose lighting using these new high powered, high efficiency LED chips. Decide right now how much you're willing to pay for the first 600-800 lumen lamp you buy for your home, then keep your eye out for it; As an early adopter, I'd gladly pay around $45 for one.