Three tact switches, three LEDs, three I/O lines
Francois AUGER & Philippe Fretaud has posted this Design Idea on EDN that shows how to drive three LEDs and scan three tact switches with only three I/O pins of microcontroller. They have demonstrated the technique using the Atmel microcontroller (Arduino), and the technique could be useful for any low pin count devices where you can run out of I/O resources easily.
3 switches and 3 LEDs to 3 I/O pins