Be Green Now is a site that hosts the carbon calculator, a tool to figure out your exact "carbon footprint" and what effect you yourself are making on the environment. It also provides a way to reduce those emmisions and go greener. Their customers have offset over 2.5 million TONS of carbon dioxide since '99. And if you go to the website, theres a nifty little box that tells you what offsetting that much carbon is equivalent too,
i.e. walking to work for so many days, removing so many cars from the road every year, etcetera.

From the webiste:

Head off into the wild green yonder. BeGreen offers an easy way to reduce your impact on global warming. Of course, it’s great to use less gas and electricity. And you can do even more, right here, right now. With just a few clicks, you can calculate and offset your carbon footprint. So what are you waiting for? Go ahead and BeGreen.