Two years ago, under pressure from the U.S. government, lightbulb makers stopped manufacturing the humble incandescent lightbulb. You can still find some on the store shelves, especially specialty and 3-way bulbs, but standard 40/60/100 watt A19s are no longer available.
Unless you stockpiled a lifetime supply of incandescent bulbs, you're probably in the market for replacements for your home. One of the available options is CFL.
CFL, or compact fluorescent, bulbs have been around for a while, and have improved since they were introduced. You can see up to 75% energy savings, and they're supposed to last around 10 times longer than incandescent. Price-wise, they're in the middle of the price range for bulbs.
One concern with CFLs is that they contain trace amounts of mercury. This does make cleanup of broken bulbs and disposal of old bulbs a bit more complicated. The EPA put together an entire website devoted to CFLs, and it has detailed instructions on what to do if a CFL breaks or starts acting up and how to recycle CFLs when you're done with them.