I just hit one of the sites that I support (which I rarely visit - must be very well built...) and was reminded of an easter egg that exists in the site that was put in before I 'inherited' the site. There is a hidden link in the site banner that plays a quick little .wav file. Some may find easter eggs unprofessional, but I think they're mostly all in good fun. So what is your favorite easter egg? Do you ever sneak them into your sites?

Here's another one that we found absolutely hilarious. We had another site that would serve random quotes in the footer. Mostly silly stuff, but our users seemed to find them amusing. So a while back we decided it would be quite funny to slip in the good old 'All Your Base Are Belong To Us' - every time we demo'd that site that quote would invariably slip in and us developers would have a little chuckle while everyone looked at us like we were crazy.