Forestle seems like a good alternative when searching the Web. Those annoying sponsored links are finally put to productive use, helping save the rainforest. As of November 20 this year about 9,250,000 square meters have been saved on the Osa Peninsula in Costa Rica.
Forestle, based in Germany, uses the Yahoo engine to bring up results. The site has been around since 2008, but seems to have a surprisingly low profile. There's an article on Wikipedia that provides some interesting details. It's nice to think that you can actually make a small difference each time you punch in a search - and the cost is nothing more than a mouse click.