DC Gearmotors are awesome!
This video demonstrates six basic ways to integrate them into your project (including Arduino and Raspberry Pi):
Materials:
Arduino
Raspberry Pi
Power Darlington Transistor
Power Darlington Transistor
H-Bridge Chip
Motor Driver
Related Videos & Resources:
Arduino Stepper Motor Tutorial!
Control Large DC Motors with Arduino! SyRen Motor Driver Tutorial
Arduino & ClearPath Servo: Moving 34 lbs FAST!