Mess with someone's printer!!!
HP Printer Fun lets you change the text of an LCD display on any HP LaserJet printer! What could you do with this awesome power? You could send something funny to the LCD. that puts a smile on people's faces, like NEED OIL CHANGE or I HAVE SWINE FLU. Or you can advertise a company event. Like, Meeting @ 3pm.
But...don't get fired!
Note that this application only works with HP printers, mostly the LaserJet variety, but some other types as well. It probably will not work with the DeskJet or PhotoSmart models (though I have no way to test them all).