The EPA maintains a list of green power companies at <a href="http://www.epa.gov/greenpower/pubs/gplocator.htm" rel="nofollow">http://www.epa.gov/greenpower/pubs/gplocator.htm</a>. It's honestly worth making the change if you can.<p>Here in NYC all you have to do is change which ESCO provides you power; I switched to ConEd Solutions two years ago. It's either 1 or 2.5 cents more per kWh (depending on which plan you pick) which works out to only a few extra bucks. Your energy is still technically the same (the electricity generated from your ESCO just goes into the general pool) but it's another step in the right direction.
I pay a few bucks extra a month to have my electric company remove however much energy I use from their conventional pool and buy it from renewable sources instead. It doesn't seem to have helped much though because they just put into service a new $2 billion coal-fired plant. :(