These are just some tips I've found save energy, which in turn helps the environment.  It doesn't hurt that you save money in the long run, too!  The below tips cost little or no money at all:

1. Your dishwasher utilizes less water per cycle than if you hand wash.  It also gives you more time for other things.  Save even more energy by only washing full loads and by turning off the drying feature on your washing machine and letting your dishes air dry.
2. Wash as many loads of laundry as you can using cold water.  The majority of energy is used to heat the water.  Also air dry your clothes whenever possible.
3. Limit your showers to 5 minutes.  Ladies: shaving takes up the majority of time spent in the shower so shave out of the sink instead.
4. Use a digital thermostat to regulate the temperature in your home.  These can be purchased rather inexpensively and are easy to install yourself.  Keep the temp in your home at a steady happy medium.
5. Keep all windows, blinds, shades and curtains closed when running your heat or air conditioning.  You might as well watch your money float out the window by keeping them open.  On that note, turn off the A/C and open those windows when it is mild outside.
6. Grow your own vegetables and herbs.  You'll save an unbelievable amount of money, plus reap the benefits of having the freshest pesticide-free produce.
7. Turn off lights as you leave a room.
8. Unplug appliances if you won't be using it again for a while.  Even if turned off, many appliances use energy just by being plugged in.  (TVs, stereos, gaming systems, computers, even cell phone chargers.)
9. Invest in a water filter.  For approximately $20 a year you can have all the clean drinking water you want.  Buying bottled water is not only a waste of money, but all that plastic can't be good for us.
10. Bring re-usable bags and totes on shopping trips whenever you can.  If you have to choose paper or plastic, don't worry about which to choose - they both make near the same impact on the environment.  It's what you do with them afterwards that counts.  Most stores have recycling boxes for bags now, so make sure you recycle.