Electronics Projects for 12-Year-Olds?

nepheles asks: "I've recently been asked to teach some electronics classes for a group of 12-year-olds. They're all new to it. Electronics always seemed boring in school, so for them, I've been looking at hands-on projects: I've considered making basic motors, steady-hand games, and Morse-code communication systems. What experiments have you seen in electronics that amazed you, and that could be recreated in the classroom? What cool things have you made that would be simple enough for a kid to do? At a meta level, how would you like to have been taught electronics?"