This applet shows the motion of holes through a crystal lattice with an external electric field applied. (Although it is actually the electrons that are moving, it is often simpler to think of the empty spaces as if they were particles moving in the opposite direction.)
The "Show electrons moving" checkbox toggles animation for the electrons. This does not affect the behaviour of the electrons or holes (save for a small time delay while the electrons are moving) and is provided merely for aesthetic value.