http://upload.wikimedia.org/wikipedia/commons/thumb/8/8f/Gestalt_similarity.svg/300px-Gestalt_similarity.svg.png

This picture shows Gestalt's similarity.

http://www.jefftzucker.com/i/jtzfig-ground.gif

This is an example of figure and ground.

http://graphicdesign.spokanefalls.edu/tutorials/process/gestaltprinciples/proximity/images/proximity01.gif

This picture is a good example of proximity.

http://z.about.com/d/psychology/1/5/9/1/closure.jpg

This picture is a good example of closure. You know what is supposed to be there, even though it isn't.