Here is some information I found regarding green energy for the consumer in the US. This was the most helpful link: http://apps3.eere.energy.gov/greenpower/buying/buying_power.shtml
It breaks down (as of May 2008) green energy providers by State.
"If retail electricity competition is allowed in your state, you may be able to purchase a green power product from an alternative electricity supplier. Some states have already implemented electricity competition. Check the Status of State Electric Industry Restructuring Activity (PDF 2.1 MB) map, prepared by the U.S. Energy Information Administration, to see if your state has passed an electricity competition law.
Even if your state is not implementing electricity market competition, you may still be able to purchase green power through your regulated utility. More than 600 regulated utilities spanning more than 30 states offer "green pricing" programs (see our map of green pricing programs). The term green pricing refers to an optional utility service that allows customers to support a greater level of utility investment in renewable energy by paying a premium on their electric bill to cover any above-market costs of acquiring renewable energy resources.
Finally, whether or not you have access to green power through your utility or a competitive electricity marketer, you can purchase renewable energy certificates (RECs). RECs (also known as green tags, green energy certificates, or tradable renewable certificates) represent the environmental attributes of power generated from renewable electric plants. A variety of organizations offer RECs separate from electricity service, that is, you need not switch from your current electricity supplier in order to purchase these certificates."