I took this project on as a present for my girlfriend, who, during the colder months, is more or less addicted to coffee/hot chocolate/tea. Her mug broke, and I was just going to get a new one for her birthday, but I wanted to add a little functionality to it. The new mug now senses and displays the relative temperature of its contents on a 10-LED blue bar display and has a rechargeable battery, which is charged through a 5.0V DC jack. Turned out pretty well, although it reacts a tad slow to temperature changes, as you can see in the video.
Coffee mug with temperature indicator – [Link]