www.freerice.com
Rachael sent me a link to this website. For every correct answer 20 grains of rice are donated to UN World Hunger Program. I am quite addicted to this game and I think I have reached about 4,000 grains of rice. It's fun and challenging.
According to web sources about 7,200 grains of rice = 1 cup. In other words not a huge personal pay off, but the more people play the more is donated. So fun!!! (it helps if you are word buff)
P.S. my highest vocab. score is 40. Good luck!