In certain instances a photo gallery is a must, for example any site that deals in tourism.
Hotel
Guest house
Attraction
Another, is where it would be advantageous to display examples of work.
Artists
Craftsmen (wood turners, potters etc.)
Sign writers
Gallery
Shown below is a small example.
This style works well in most layouts. When the thumbnail is clicked the full size image opens in its own window, which means you do not have to keep going back to the main gallery.
