FreeRice

FreeRice is a website run by the United Nations World Food Program to help fight world hunger. In addition to helping people all over the world, FreeRice was built to help improve vocabulary (and now other subjects, too). For every word (or country, math problem, translation, etc.) you get correct, ten grains of rice is donated with the help of FreeRice's sponsors. And now, you can take it even farther you can download the FreeRice Toolbar and, with ten legitimate searches, you donate an extra 5,000 grains of rice per day! According to FreeRice's FAQ's,
"The rice you donate makes a huge difference to the person who receives it.

According to the United Nations, a child dies every 6 seconds from hunger related causes.

Though 10 grains of rice may seem like a small amount, it is important to remember that while you are playing, so are thousands of other people at the same time. It is everyone together that makes the difference. Thanks to you, FreeRice has generated enough rice to feed millions of people since it started in October 2007."