Crispin Flowerday points out another: type "gegls from outer space" in the Run Application dialog. This was the best ever, I think.
Paolo Borelli pointed to another easter-egg: Just type "free the fish" in the Run Command Dialog. Woohoo!
Okay, thanks to James Henstridge, I have found an easter-egg in Zenity. Yay!
I'm Enver ALTIN, a software developer at Cellenity.