Best procrastination site ever. You've seen those "click here to donate a cup of food" sites? Here's a better version. Take an online vocabulary quiz. For each correct answer, the sponsors donate 20 grains of rice. Right answers get you harder questions, wrong answers get easier ones. The top levels will challenge just about anyone, hence the afternoon killing potential.
(For the skeptics, even tiny amounts add up. There are 29,000 grains of rice in a pound. Donations to date add up to shiploads.)