The U.S. Department of Energy's National Renewable Energy Laboratory Website
Visit this one first. This site is fantastic! Start with "Clean energy basics" and explore from there. You can find links here explaining how photovoltaics work, how to select a home solar hot water heater, how renewable energy can provide for transportation (electric, propane, and transit on demand), how wind energy and solar thermal electric energy can help our country meet its energy needs. This site demonstrates the high level of sophistication of renewable sources of energy that can take the place of fossil fuels right now. There are some outstanding photographic images of solar and renewable energy technologies that you can search and download.
http://www.nrel.gov/

Florida Solar Energy Center
Another great website about solar and renewable energy sources. Check out the alternative fuels for transportation links and the photovoltaic links (both are excellent) and the Space Coast Clean Cities program link.
http://www.fsec.ucf.edu/

EPA's Energy Star Homes Program
Want to buy an energy efficient solar home? Here's how you can do it! ENERGY STAR Homes use at least 30% less energy than required by the national Model Energy Code while maintaining or improving indoor air quality. Are you a builder? Submit you plans to the EPA and get an energy star rating.
http://yosemite1.epa.gov/estar/homes.nsf/HomePage?OpenForm

The University of Wisconsin-Madison College of Engineering's Solar Energy Lab (SEL)
This is the oldest solar energy research lab in the country. They accept graduate students interested in solar energy engineering and design.
http://sel.me.wisc.edu/

Solstice. The Internet information service of the Center for Renewable Energy and Sustainable Technology (CREST)
This is a site for Sustainable Energy and Development Information. An excellent source of information about renewable energy, solar energy, and solar hot water heating systems.
http://solstice.crest.org/

The Home Energy Saver (US EPA Sponsored)
The information and interactive tools you'll find here can help you figure out how to save hundreds of dollars on your energy bill, and prevent pollution too. This site is still being developed, but it provided some excellent information about how you can save energy in different regions of the USA. There are rating lists of energy efficient appliances and heat pumps. There is an interactive energy audit (you input data specific to your home) that tells you what your energy bill should be and could be if you made all the improvements that they suggest. A very interesting site for the homeowner (or future homeowner) who wants to save money and energy.
http://homeenergysaver.lbl.gov/

Sandia National Labs Renewable Energy Web Page
Look here for information about research into renewable energy technologies, including solar thermal, geothermal, wind and photovoltaics. Great images of The National Solar Thermal Test Facility (NSTTF), with the Central Receiver Test facility, better known as the power tower, which is an 8 Megawatt solar-thermo-electric generating facility. This technology is expected to be commercially competitive with other energy sources. Also, good photos of a 34-meter wind turbine.
http://www.sandia.gov/Renewable_Energy/renewable.htm

International Geothermal Association
An information-filled website about geothermal technologies around the world. Pictures and descriptions of the world's geothermal electric plants.
http://iga.igg.cnr.it/index.php

U.S. Department of Energy, Energy Efficiency and Renewable Energy Network
Find general information on renewable energy and many links to other internet sources.
http://www.eren.doe.gov

International Energy Agency (IEA)
IEA was formed in 1974 as an autonomous body within the Organization for Economic Co-operation and Development (OECD). The Agency maintains an emergency system for dealing with oil supply disruptions and a permanent information system on the international oil market. Recently, attention has been paid to strengthening the link between environment and energy policies. The web site contains IEA publications, statistics, and information about energy, economics, technology, and climate change.
http://www.iea.org