I used to leave the porch light on all the time. It was a huge bone of contention with my husband because he would come home and turn off the light, and then I'd get home and it would be dark. We switched to light bulbs with light sensors for inside the porch and motion detector lights for outside. Now we're both happy and saving money and energy!
I also switched from plastic water bottles to reusable ones, and recycle everything I can.
I'm looking for more ideas of things to do. What steps have you taken to go green?