I don't know of any. You could call the screen privacy feature in LOS an "easter egg" although it's probably just a feature (and maybe even documented somewhere). Shift-option-keypad 0 smoothly dims the screen to black, then the same combination undims it when you're done.
Now that I have a way to use the Lisa's video out port, I know what happens to the fridge light when the door closes the mouse pointer when the screen is fully dimmed: it turns into the hourglass. This makes sense: that way the mouse doesn't cause any trouble if you click it when you can't see anything.
For anything else, one approach might be to comb the Lisa Office System source code and look for any hints of easter eggs there.
