Post your time-wasters here!

I have a friend who has to stay awake all night on Tuesday for medical testing purposes. I promised her some addictive online games to keep her busy. I have a couple, but I don't know if it's enough to get a person through a sleepless night. Do you know of any addictive online games, or other websites that are very conducive to wasting one's time? If so, please post them in my comments here!