This website is great: http://www.freerice.com
It has a vocabulary game on its main page. Each time you get an answer correct, not only do you move up a level, but you have also donated 10 grains of rice to charity. This might not seem like that much, but after you have played it a lot, it adds up to quite a bit. If you look at their Totals, you can see how much rice they have donated each day. The amount is huge, and they have only been running since the 7th October 2007. The total grains of rice donated to date is 3,531,907,160, an astonishing figure.
How does it work? Each time you click on an answer in the game, it loads a new page, with new advertisements at the bottom. All the revenue that they earn from the advertisements, each time you load a new page, is donated in rice to the United Nations World Hunger Campaign. Still, if you get the question wrong, your 10 grains of rice from that question is not donated, so it also in a way improves your vocabulary.
There are 50 levels, although it seems that not many people can get past 48. I managed to get up to 34. Let me know how you get on!
