Just read this one on BoingBoing. Last.fm's robots.txt is pretty cool go here Here are the juicy bits Disallow: /harming/humans Disallow: /ignoring/human/orders Disallow: /harm/to/self Code (markup): Asimov's laws of robotics.. Amazing actually ! Have you seen any such interesting robots.txt files?
There is a website with loads of funny robots.txt snippets they have found on other sites. Google quite often do something amusing with theirs.