Unity

Proximity:

The 3 ladies close together are a great example of proximity.
http://www.thefrasergallery.com/artwork/DouglasMalone/Proximity5.jpg

Repetition (emphasis on similarity):

This Warhol piece featuring Marilyn Monroe shows repetition with an emphasis on similarity. Her image repeated over and over makes this happen.
http://persuasiveweb.files.wordpress.com/2009/06/repetition_warhol2.jpg

Repetition (emphasis on variety):

The similar square pattern with no color pattern shows repetition with an emphasis on variety.
http://homepage.mac.com/credmond/images/Repetition.jpg

Continuation:

The leaf crossing the 'H' show good use of continuation.
http://graphicdesign.spokanefalls.edu/tutorials/process/gestaltprinciples/continuation/continuation_a.gif

The grid as organizing factor:

The grid of signage and buildings make good use of the grid in the city.
http://invisibleman.com/nyt_directions_500.jpg

An example of a chaotic, unreadable image:

There is no real organization in the picture shown here. It seems to me to be almost evil looking. I like it!
http://www.abm-enterprises.net/fractal-art/chaos-theory-wallpaper.jpg

An example of a non-objective expression of unity:

The signs gathering in the middle of the circle show unity.
http://www.okanaganarts.com/news/data/upimages/1262979595-1.jpg

An example of a figurative expression of unity:

The 4 ladies arm in arm are showing the figurative unity.
http://artfiles.art.com/5/p/LRG/35/3591/7BU2F00Z/monica-stewart-unity.jpg