A new calculator, thanks to Greg!

http://www.americanforests.org/resources/ccc/

Many calculators on the EPA webpage, as well as its own:

http://yosemite.epa.gov/oar/globalwarming.nsf/content/ResourceCenterToolsCalculators.html

#individuals EPA basic calculator also includes how to mitigate with specific actions

http://globalwarming.enviroweb.org/games/yourscore/yourscore2.html

simple calculator and games

http://www.americanforests.org/resources/ccc/index.php

plus how many trees you need to plant to offset

http://safeclimate.net/calculator/

simple calculator

http://www.airhead.org/

simple calculator

Plane trip calculator

http://www.chooseclimate.org/

plus interactive climate model

http://travel.500ppm.com/

C offset options for plane travel