Unfortunately the Arduino specification doesn't include a true digital-to-analogue converter, however we do have the pulse-width modulation with analogWrite(). You can, however, create a more accurate rendition of a DAC using external discrete components. The people at 'provideyourown' have demonstrated how to do this quite easily. Using a simple resistor-capacitor circuit a reasonable result can be generated.
When creating more complex circuitry such as a digital-to-analogue converter for your Arduino - consider our range of ProtoShields. From the tiny LeoStick to the Mega range, we offer a complete range for you to work with.