follow this link to find out about rotary encoders which are really useful sensors to work out the speed of rotation and position or angle of rotation of a shaft or axle. I first used them on an installation with a bike to work out how fast people were pedalling and using that control the speed of a quicktime movie. to read more click here.
I have been doing some work with an electronic compass (CMPS03) and using it with an Arduino. Compasses are useful in navigation systems and also for determining general motion and rotation. To read more click here.
See how to use a h-bridge with a DC-motor to control the direction of rotation. Also see how I have used it with a rotation sensor (quadrature encoder) to control rotational position to a really precise degree. To read more click here.
Stepper motors offer a high degree of precision of angular rotation and are quite simple to control. To see some of my findings about using and controlling stepper motors click here click here.
Servo motors is an essential device in physical computing, if you want to make things move precisely then servos are the way to go. To see how I use them click here