The staff over at Instructables have designed and published their plans on how to make a nice Arduino-controlled waveform generator. Although you won't be replacing commercial equipment with it, the project is very easy to work with and they have also included plans for laser-cutting an enclosure to help move the project from the breadboard to a usable tool. You can generate sine, sawtooth, pulse and triangle waves of between 1 and around 50 kHz. Apart from the Arduino the rest of the circuitry fits nicely on an protoshield.
When recreating the waveform generator 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.