Wren - Offset your carbon footprint by saving rainforests
Klima - Go carbon neutral
Trip to Carbon - A carbon footprint calculation API for travel.
Capture - A great free screen capture utility that allows you to capture either a window or the desktop and save it to either a file or the clipboard.
Offset List - Companies that are offsetting their carbon emissions.
Website Carbon Calculator - Find out the how much CO2 your website emits