Forestle
For searching the web using Forestle was also essentially CO2-neutral: Of course the server computers used by Forestle, the connection network, and the computer of the searching users need electric energy and thus create emissions of carbon-dioxide; but Forestle purchased an equivalent amount of renewable energy certificates. The certificates are purchased from a part of the 10% of money left after buying rain forest. This makes Forestle one of the few web search sites that are "green certified".