My office mate just showed me another way to kill time at work (in three-minute increments only!). I can take a break from work, all while feeding others and improving my vocabulary.
Go to www.freerice.com and all you have to do is choose which definition of the given word is correct. With every correct guess, 10 grains of rice are donated to the United Nations. Not only will you improve your vocabulary, but you'll be helping others. Guessing from the different corporate logos that appear on the bottom of the page, this thing has a lot of big-name sponsors.
And if you're like 99% of all people and wish you could get rid of the excess junk mail you receive, there is a way to help. You know the National Do-Not-Call List? Yeah, there's a Do-Not-Mail List that is maintained by the very people who make the junk mail. Their reasoning is that it will save them money to only send junk mail to people who actually want it. So go here and sign up!