People have been coming up with clever 404 error pages for their web servers for a while, including Haiku and whatnot, but here's one that uses Javascript to spit dialogue out at you, one sentence at a time.
In the style of Marvin, the depressed robot from Hitchhiker's, try this page, and imagine you were honestly looking for something useful on that site:
http://www.avsforum.com/asdf