Kermit the Frog had it right. There are a lot of 'green' things that are hard. It's hard to get out of your car and ride a bike or take mass transit (even if those are a generally a lot cheaper). It's hard to find truly green building materials; there's not as much variety yet, and in some cases they're more expensive (though in most cases those things pay for the difference over time).
But a really easy green thing to do is use compact fluorescent lights instead of incandescent lights. It's hard to spell, so call them CFLs and say floor-ess-uhnt. And you don't have to spell it when you grab a package of them at your local hardware store. Recently, Seth Godin challenged bloggers to push the benefits of CFLs, as only 6% of the households in the U.S. are using them.
They take less energy than incandescents. Despite having a small amount of mecury in them, they put less mercury into the environment because burning coal for power (which is where large amounts of the power in the U.S. comes from) puts out (literally) tons of mercury. They give off less heat (not a big deal in winter, but no sense making your A/C or fans work harder than they have to in summer). They last longer so you don't have to get that step ladder out so often. Unlike fluorescent lights of old (though the long tube ones are still this way), they come on immediately and don't flicker.
And despite a higher up-front cost, over their lifetime they'll save an average of $66 each. We have a fairly small house, and I can think of 30 bulbs -- $1,980 of savings.
What's not to like? (OK, those annoying plastic blister packs they come in, for one.) But it can be easy to be green.