1. Ecosia: www.ecosia.org
Eevery search saves about 2 m² of rainforest, according to Ecosia which cooperates with the WWF. It's results are based on Bing and Yahoo.
2. Znout: www.znout.org
Accordning to Znout, you can make your Internet searches CO2 neutral. Based on Google.
Next two these two, there are more green search engines in the market. Even they don't have built in some fancy Google features the green alternatives are certainly good enough for usual searches. Computers are a significant and growing consumer of electricity and therefore producer of CO2 and climate change.
"Electricity generation required for information and communication technologies is currently responsible for 2% of global CO2 emissions" (Techcrunch)I just switched to green 'googling' and made one of them my default search engine. Just waiting for the moment when giant Google wakes up by searchers walking off green and then starts greening itself. Goliath, the green Davids are coming.
Happy green searching.