This page is all about fun or weird things to do on the web if you are just killing time (or avoiding work). Feel free to suggest more by adding a comment.
Orisinal - more fun games! This has a whole bunch to choose from. Thanks to stompeers for the linky on this one.
Jason Kottke - "has the most amazing compendium of things on the Web to view and consider, when you are in the mood for some serious entertainment -- or to kill time. :)" - Added from comment by Sameer
Falling sand game - mesmerizing, as you affect falling sand streams.
Ask A Ninja - all the rage and basically in the same vein as HomeStarrunner without the flash.
Google Image Labeler - You label images for Google search in a little collaborative game with other folks online. You are basically trying to both pick the same term to describe a picture. It's pretty addictive.
KrazyDad's Experimental Colr Pickr - pick a color and it will pull a group of Flickr photos that match.
LibriVox - either listen or learn to record Public Domain books.
Wikipedia's Random Article link - this is totally geek, but I am addicted
Homestarrunner - Check out the "first time here?" button and then go watch StrongBad's emails. [Bonus for those who really have time to kill: Burning Horizon's list of Strong Bad Email Secrets!]