I was just introduced to freerice.com and was instantly hooked.
Basically, you answer multiple choice questions on a subject of your choosing (Mine? English vocab., natch...) and for every correct answer they donate 10 grains of rice through the world food program. Not bad, eh? But DAMN, some of the questions are hard! They make you WORK for that rice!
Like, dude, "acidulent?"
Oh yeah, sour. Of course, sour. See, I knew that... *EEP!*
Now that's some hard-earned rice ;)