Tankless or on-demand water heaters
For homes that use 41 gallons or less of hot water daily, on-demand water heaters can be 24%-34% more energy efficient than conventional storage tank water heaters. They can be 8%-14% more energy efficient for homes that use a lot of hot water-around 86 gallons per day. You can achieve even greater energy savings of 27%-50% if you install a demand water heater at each hot water outlet. (U.S. Department of Energy)
Eliminate Phantom Load Energy Use
A "phantom load" is the energy that's sapped by appliances when they're plugged in, but not on. Use power strips or manually unplug DVD players, computers and cell phone chargers to save electricity from disappearing without a trace. In the average home, 40% of all electricity is used to power home appliances while they're turned off. If all phantom loads in US homes were stopped, we could shut down 17 power plants. Power strips with surge protectors make it easy to "unplug" many appliances at once.
Water-efficient shower head
Reduce the amount of water used without reducing shower pressure. Equipping each faucet in your home with an aerator is another extremely easy and inexpensive way to reduce water waste.
Low-flush model use 1 to 2 gallons per flush instead of the usual 3 to 5
These use little or no water and processes toilet waste for reuse as valuable compost. Modern, sleek versions available that can be installed in any bathroom.
Energy efficient light bulbs and fixtures
It's no secret that only 10 percent of the energy used by incandescent light bulbs produces light. The other 90 percent is lost as heat, which in the warm months is doubly wasteful, as more energy must be used for home cooling. Energy Star-certified compact fluorescent lights (CFLs) use at least 2/3 less energy than incandescent bulbs while providing the same amount of light over a life span up to 10 times longer than their incandescent rivals. Total energy savings can add up to $30 or more over each bulb's lifetime.
Not only do you save electricity and reduce greenhouse gas emissions but you get free natural lighting.
Global production of solar PV cells, which turn sunlight into electricity, has risen six-fold since 2000 and grew 41 percent in 2006 alone. -- Getting more affordable
Grey Water Capture
Capture and reuse sink water to flush toilets saving 10 - 20 gallons of water a day. There are many such products on the market.
Replacing old boilers with more efficient units (old boilers can account for more tan 85 percent of a building's energy waste), installing double-paned windows, insulating the roof, and installing motion sensors to common-area lights.