In the Maker Shed: EZ-Expander Shield Kit
Need more digital outputs on your Arduino? Check out the EZ-Expander Shield from the Maker Shed! Using the two 74HC595 shift registers, you can add up to 16 new output pins (numbered 20-35.) The shield itself uses 3 existing Arduino pins to operate (pins 8, 12, and 13), so overall you get 13 additional output pins to use.