Now I stumbled upon this site and it's a great idea. FreeRice.com is an online word game that tests your vocabulary and for every question you get right the makers of the site donate 10 grains of rice to be distributed to the poorest nations of the world via the United Nations. Ten grains doesn't sound much but since going online in October it's donated 50,000 grams of rice, which is quite amazing. So if we all play just a little a day then it will make a huge difference.
The only catch I can see is that the site displays three small adverts at the bottom of the screen which are unobtrusive and you don't have to click. Go and play, improve your vocabulary and help the starving at the same time, you can't lose.