The Konami Easter Egg plugin lets you add a YouTube video of your choice and a hidden messages to your website. Only people who know the secret code can see your message (unless they are poking around in the source code of your page, that is). By default, the secret code is the classic Konami cheat code (up up down down left right left right b a enter) but you can change it to anything you like. You can also customize the css to change the colors on your hidden page.
This plugin is made possible by George Mandis whose Konami-js code can be found at http://code.google.com/p/konami-js/