Most StackExchange websites (even some currently in beta) have some sort of Easter egg. These are usually applied to the chat room, so that when you send a specially-crafted message the chat room does something interesting.
RPG has dice.
SuperUser has Clippy.
Gaming has Asteroids.
rm -rf /.
And there are some others, documented and undocumented.
Our regular chat crowd has yet to stumble across any for our site, so we're guessing there either isn't one or we're just not being told. Under the former presumption, I'd like to suggest that we put some proposals here. I'm not aware of whether or not the communities actually get to choose their Easter egg, but I figured we could at least make sure there's some input available for whenever SEI decides to give us one.
So, what Easter egg would you like to see? Only one suggestion per answer, please, to allow for voting to be accurate.