Plenty of people enjoy coffee and a good many enjoy LEGO too, so it was only a matter of time before the two were combined. The Build-On Brick Mug is a coffee cup covered in studs and holes that attach to LEGO and other building blocks to customize it however you want.
The mug is compatible with LEGO, PixelBlocks, Mega Bloks, KRE-O, or K'NEX Bricks – but you'll have to provide those yourself. The blocks can be combined to customize your cup of coffee any way you want. You could construct an attached plate to hold a doughnut, for example, or work in some LEGO Mindstorms to create your very own robotic coffee mug.
One possible drawback is that the odd shape (along with the risk of having a LEGO minifig end up in your nostril) could lead to spillage. Also, while it has no problem holding hot drinks, the mug is not microwave or dishwasher-safe.
ThinkGeek is selling the Build-On Brick Mug for US$19.99.