I just discovered a nifty little program called Granola. Yes, like the grain/seed (I don't care which).
What it does when run is it optimizes the CPU in your computer to lower its energy usage without actually harming performance. As such, the differences are can be quite minor depending on how you look at it. I am running it right now, and it tells me that if I run it all the time my computer will be on (I actually turn it off at nigh - even better), I will save 161.4 kWh in one year ($19.35 USD). This sound like a lot, but my CPU is a somewhat old Intel Quad Core Q6600. It's good, but it's not comparable to say, the i series of processors.
It makes sense that the best thing will be to turn your computer off when you are not using it, but if you are using a laptop and put it to sleep, or leave it on because you will use it soon, then you might consider running this little application. And it runs in the background, so you don't notice it.
Here's the link to their main website: http://grano.la/
You also might be wondering why I posted this in the World Issues section versus the Smartypants section, well I believe that taking care of the planet is a world issue to be solved by humans. And in this case, I guess that every little bit can count.