The 74HC595 is a 8 bit serial to parallel shift register. It is exceptionally useful when you need to expand your inputs. This allows you to convert 1 serial byte into 8 outputs. The 74HC595 also allows you to cascade these devices for more bits. You will need three pins, serial, serial clock, and a latch.
Spec Sheet: http://www.ti.com/lit/ds/symlink/sn74hc595.pdf
alt-Spec Sheet: http://www.onsemi.com/pub_link/Collateral/MC74HC595A-D.PDF
Voltage In: 2V ~ 6V
Supply Current: <80uA
Current Output (Max): mA
Output Type: Tri State