At FreeRice.com, you play a simple word game and for each correct response, the site’s advertisters donate 20 grains of rice to the United Nations World Food Program. If you know your words, it can really add up quickly! I donated over 1000 grains of race in just a few minutes yesterday.
Go give it a try. It will make you smarter and help the world’s poor. (Thanks to Luke for the tip!)