Use an H-Bridge to drive a DC motor in two directions. The H-Bridge contains four half bridge drivers, enough to drive two DC motors in either forward or backward independently – perfect for making a roving robot! The SN754410 H-Bridge and L239D H-Bridge chips are pin-compatible, but this one integrates flyback protection diodes, making it simpler to wire up.
Download the L293D H-Bridge Datasheet (PDF)
Buy the Texas Instruments L293D H-Bridge IC from Amazon, Adafruit, or Newark.