If you're interested in adding more analogue-to-digital ports to your Arduino board but don't want to pay extra for a Mega - or would like a true digital-to-analogue converter, check out John's latest tutorial about the NXP PCF8591. It's a convenient part that has four 8-bit ADCs, a single 8-bit DAC and can also operate as a differential ADC if so required. All the required Arduino sketches are provided and explained, having you up and running in no time.
Fitting the PCF8591 to a protoshield would make an interesting addition - and when adding external circuitry to your next Arduino project, you'll need a protoshield to mount the external circuitry. In doing so, consider our range of ProtoShields. From the tiny LeoStick to the Mega range, we offer a complete range for you to work with.