This the most addicting thing I have done lately. Test your vocabulary, and for each one you get right, 10 grains of rice are donated to the UN World Food Program. It tell you what level you are averaging based on on what you get right. I averaged about 39 (out of 50) and my highest was 44.
Seriously, though, you won’t be able to stop.
(unabashedly stoled from Patrick)