Electrick made this interactive LED candle. It uses an Arduino and a simple aluminum foil switch to control the flickering. There are more photos and the code on the web site.
The LED glows, but when I blow across a simple little switch I tossed together, the LEDs flicker like a candle does when you blow on it! Soon after the LEDs return to normal operation. I know this isn’t much, but then again its my first Arduino project.
Read more about Arduino powered LED with breath switch.