We bought the nest thermostat for our new house (they didnt have a programmable one), and we LOVE it. You can track it's energy usage, and it has different options to make your house even more energy efficient. You can also control it from your phone, so like for us, we keep the house fairly cold in the winter when we're not home....and now we can turn up the heat just before we leave the office at the end of the day!
Other ideas: we've been making our own iced tea and cooking more frugally using fresher in-season ingredients. When we do cook, we make enough for leftovers so that we don't have to use the oven/stove EVERY night. We also crack the oven open when we're done cooking to heat the kitchen a little =)
We tried filling a water bottle and putting it in the toilet tank to reduce water waste, but our toilets didn't really like that solution. they're pretty old and finicky to begin with.
We keep an extra recycling bin upstairs in the office to promote more recycling of paper items.
In the spring, we're planning to plant a vegetable and herb garden, and perhaps start a rain barrel to water the garden. Down the line, we are also hoping to investigate solar panels...even just small ones might help us out =)