Back in October 2013, there was a big ol' dumpster in a parking lot. Its surface was banged and worn by years of use, and the various rust and scratches patterns were beautiful.
Since no designer's library of resources is complete without rust textures, I went ahead and snapped as many shots I could from the rusty beast. The result is a series of 45 textures sized at 3264x2448 pixels that go from subtle speckles in the paint to heavily destroyed and rusted metal.
These should cover a wide array of your rusty textures needs. Don't hesitate to share with me how you use these!