Check out this awesome business card by Joe Colosimo:
bcard is an experimental attempt to make cheap electronic business card on a thin PCB. The main goals are for it to be:
- not gaudy
- not stupid
Joe’s design incorporates a capacitive touch sensor with some blue LEDs around the corners. The blue LEDs are actually mounted upside-down so that the card fluoresces.
Cost of parts is about US$1.80 in quantities of 25 (at Digi-Key prices). At quantities of 100, the cost per board is US$1.54. The majority of the cost is in the 4 LEDs and the microcontroller. You can shave off a few cents by going with an ATTiny4 instead of an ATTiny10. Check out the full details plus links to GIT repos etc here.