P.U.R.E. is the program I have been participating in for a few months now through my electric company, AmerenUE.
Essentially, what happens is that 100% of my home's electrical usage is offset with clean renewable energy; which in the Midwest comes from wind power and other sources.
While my electric bill is modest due to the fact that I try not to be wasteful to begin with (turning off lights when I'm not in the room, using CFLs, etc), I wanted to make sure that even my modest energy usage wasn't wasteful. Generally, it cost me about $5-$15 a month to participate in this program, depending upon my usage for the month.
I know times are tough due to $4 gas, etc; yet if you can I highly recommend you inquire with your local energy company about similiar programs. It does make me happy to know that I am doing my part for the future.