I have created this mockup to be used with Photoshop in conjunction with the Bulkmockup Plugin application, you can purchase it here:-
 
BULK MOCKUP PLUGIN
 
The mockup template offers a size guide to your customers, for example if you sell fabric you could show the scale of each design with a click of a button... no more tedius drag and dropping in each design.
 
Although as yet this mockup cannot adjust between sizes and that is why I have included 4 templates for you to use and includes a watermark so you can use online -
Two Size in 1
12x12 inch
8x8 inch
6x6 inch
 
Includes an How to Use Guide