I'm sure most of you have seen the banner ads all over the internet by now, but I thought this was pretty cool and worth sharing.
www.freerice.com
You play a vocabulary matching game and for each word you get right, the website, using ad revenue, donates 10 grains of rice to hungry people all over the world. Since October 7th, 2,840,667,010 grains of rice have been donated. It all goes through the United Nations World Food Program, so you don't have to worry about some corporation running off with a million dollars worth of rice making hackey sacks.
If you want to add a bit of competition to it, post your highest vocabulary level and how many grains you've donated.
I just started a few minutes ago, but I'm at 600 grains with a vocab level of 40.