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.

Led Birthday Candle
From the MAKE Flickr photo pool
The LED birthday candle