FreeRice

If you want to do a good deed and build your vocabulary, you've come to the right place. Other sites give away charitable donations for little more than a mouse click, but FreeRice makes you earn them. The site challenges you with word quizzes and pledges to donate 20 grains of rice to the U.N. World Food Programme for each definition you get right. (The words get harder the longer you play.) To do more, check out the Hunger Site, which donates to relief agencies Mercy Corps and America's Second Harvest in exchange for your visit.

—Anita Hamilton