The previously posted rust metal backgrounds and grunge textures became quite popular, so assuming that you designers need this sort of stuff, here are some more free royalty-free images of that kind:
A classic, burst rust bubble (my engineer friends get really excited about this sort of damage). These stock photos were not sharpened, so you may want to apply a little bit later in your Photoshop designs.
Download these grunge textures by clicking on the pics here and use them as royalty-free images in your creations but please don´t re-distribute or re-sell the photographs themselves (I want to keep the licensing terms as liberal and simple as possible.)
Another close-up photo of a nice orange rust bubble with a grunge paint background.
