With a little research and some time you can easily determine how toy remote-control cards can be hacked into and controlled via an Arduino. Once such example has been demonstrated by Instructables user "FernOrtega" who added an infra-red distance sensor to the front of a toy car as part of an obstacle-avoidance system. As part of this project they have explained how they determined the control lines for the car, and also how to create a motor-control circuit for an Arduino using SN754410 H-bridge ICs.
When adding your own circuitry for an Arduino-based project such as the hacked remote-control car above, 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.