I thought this might be an appropriate topic for the day.

My favorite is probably the first I ever found. I love it when you can make Gabe in Gabriel Knight 3 sing the theme song from the musical Oklahoma! (LOL!)

I liked the skeleton programmer at the end of one of the paths in Treasure Island.

I'm probably a bit sick in the head but I can't forget naked Conor in King's Quest VIII, just covered with a leaf, keeping storing lots of staff on himself

I liked in Kings Quest 2 when you looked in the hole on top of the mountain how it went into a Space Quest promo.
I also like in Zak McKracken and the Alien Mindbenders how if you messed up the security code they switched to a jail cell and it said that you really should purchase a legal copy of the game.
Gamespot had an article on the greatest Easter eggs in gaming at one time.

My favourite egg is in Lifestream. There's a wall panel puzzle where, if you repeatedly click on it, your character (a priest) goes into a disco song & dance routine. "It looks like something's missing here! It looks like something's missing here!" Hilarious.