Free Rice
Free Rice is a vocabulary testing game that adjusts itself to your level of language skill - the more questions you get right, the harder the questions. But the main point of the game, and the reason you should head over and play for a while, is that for each question you get right 10 grains of rice are donated to a hungry person through an international aid agency. It doesn't sound like a lot, but the more that you play, and particularly the more of you that play, the bigger the donation will be. Head on over, play, and save lives now
http://www.freerice.com/index.php