Your total personal emissions
See how your personal choices may affect the climate.
To measure the footprint of your personal lifestyle, the CoolClimate calculator (Flash)—an ongoing PhD project from University of California, Berkeley—assesses everything from the food you eat, to your mode of transportation, to how you spend your money on clothes and furniture.
http://bie.berkeley.edu/calculator.swf

The Environmental Protection Agency has a fairly rudimentary Personal Emissions Calculator that looks at transportation, energy use, and waste produced. The site also gives you some greenhouse gas saving tips, showing how much you would save by replacing incandescent bulbs with compact fluorescent light bulbs, buying more efficient appliances, or turning down your thermostat a few degrees in winter.
http://www.epa.gov/climatechange/emissions/ind_calculator.html

How much energy is your home using?
Give yourself a free audit (the IRS shouldn't get all the fun) and see how to lower your energy bills.
If you are looking to cut down on your electric bill, heating expenses, and household carbon emissions, look to the in-depth (and fairly complex) Home Energy Saver calculator from Lawrence Berkeley National Laboratory. This calculator works as an online home energy audit, telling you how you can make your home more efficient and what government tax incentives or efficiency programs will help you get there fastest.
http://hes.lbl.gov/

Plane, train, and automobile (emissions)
Find out how much you emit getting from here to there, and read about your public transport options.
The Individual Emission Calculator from Travel Matters part of the not-for-profit Center for Neighborhood Technology, gives an up-close look at your transportation emissions throughout the year. After you find out what you put into the air, you can weigh the public transportation options in your area and see how much they emit to compare with your current footprint.
Calculator: http://www.travelmatters.org/calculator/
Planning: http://www.travelmatters.org/calculator/transit/