Wren - Offset your carbon footprint by saving rainforests
EcoCart.io - Free e-commerce plugin for merchants to offer carbon neutral orders to their customers.
YAYZY - Track the carbon footprint of each purchase in real-time
Klima - Go carbon neutral
Treeapp - Plant a tree for free, every day, in less than a minute
Neutral - Offset your carbon emissions, right from your shopping cart