Alliance to Save Energy is a coalition of prominent business, government, and environmental and consumer leaders who promote the efficient and clean use of energy worldwide to benefit the environment, economy, and national security. The site also has tips on how to reduce your utility bills.
Environmental Sciences Division of the Oak Ridge National Laboratory. From large-scale field experiments, to laboratory studies, to advanced computation, the Environmental Sciences Division seeks to understand how the use of energy affects the environment.
American Wind Energy Association has information on wind energy and a list of small wind turbine manufacturers.  All you need to get off the grid!
Natural Energy Systems, Inc., the Renewable Energy Engineering Company. They sell solar panels and other products to help you use renewable energy sources. Has a great description of types of home solar systems.
Trace Engineering sells inverters for renewable energy systems.
Creative Energy Technologies has an on-line catalog of energy saving/earth friendly products, including solar panels, solar-powered flashlights, energy-efficient appliances, etc.
Jade Mountain, Appropriate Technology For Sustainable Living. Has a great FAQ on solar power.