I just stumbled upon this unusual site called http://www.freerice.com/

The site provides an opportunity to help the hungry and covertly to expand your vocabulary.  For every word you correctly identify 10 grains of rice are donated.  Each time you get a word wrong it tells you the correct answer and lowers the difficulty.  As you get more write the difficulty goes up.

So for all those wordsmith social activists this is the site for you.