Easter Eggs: 101 of Them

"The 101 Coolest Easter Eggs Hidden in Your Software, DVDs and Video Games"
IT Security editors (April 3, 2008)

"Photoshop CS2: Merlin Li ... : Hold down both the Alt key and the left mouse button, then move your mouse over Palate Options in the Layers window. Let go of the mouse, and Merlin appears."

to

" 'Dark Castle': Interesting Treat in Main Hall: Go to the Date And Time function under the control panel, and set the date to any Friday the 13th. When you start up the game, you'll see the added effect in the main hall."

Quite a few are fun. At least one is noxious, at best.