This is kind of fun and enlightening: a kids' carbon footprint calculator.
I checked out some adult varieties but they required that you know specific values, such as how many km you travel to work, and how many kilowatts you use in hydro, etc. I don't have immediate access to that info, so I kept browsing the net until I found the kids' version, which is a lot more basic.
As I was going through and answering each question, common sense told me what the greenest answers were. This made me think that the key to using a tool like this is not so much to get my "green score" but to consider each point: what is my answer v.s. what could I do better.