Monday coffee mug

A mug that changes into a smiley face when you pour your hot coffee in it: Monday Mug, from The Cottage Industry:

Difficulty getting up in the morning? Finding it hard to start work at the office?There's nothing that'll get you going first thing in the morning like a hot cup of coffee. Before this moment you might as well not bother. At THE COTTAGE INDUSTRY we call this the 'Monday' moment...and we've invented a mug to go with it. The cold mug shows a rather tired looking face on a black background. When you pour in the hot coffee, the mug's appearance quickly changes. Within a minute, the black mug transforms into a happy spritely smiling face. Of course it also works with tea or hot chocolate!

Also: On/Off mug