Some visual illusions

A more comprehensive list can be found here :

The Müller-Lyer illusion

The Cafe wall illusion

Hermann's Grid

If your eyes follow the movement of the rotating pink dot, you will only see one color, pink. However. If you stare at the black "+" in the center, the moving dot turns to green. But if you concentrate on the black "+" in the center of the picture, all the pink dots will slowly disappear after a while.