FreeRice which I first came across via Ms. K  is a neat concept. Play a vocbulary game and if you get a word right, 10 grains of rice are donated through the United Nations World Food Program (WFP) to hungry people.
Even if you don’t have altruistic motives and have enjoyed vocabulary games, you can still play. The site’s servers do not know your intentions.
The words get increasingly difficult as you get them right and the game is addictive, so it’s perfect during work meetings, after-lunch work at the desk, and other working activities.
Did I mention that it was free? Go play
: It just sounds cool to say it this way.