What is the current rating of your DC motor? If it is less than 1.2A per motor then you might wanna consider using this Adafruit Motor/Stepper/Servo Shield for Arduino v2 Kit [v2.3] : ID 1438 : $19.95 : Adafruit Industries, Unique & fun DIY electronics and kits
It is the easiest and simplest way that I can think of. Everything is already pre soldered and the library code is ready to be downloaded from Adafruit official website. They have a very good documentation on that shield too.