I have recently been working on texturing for UV mapped models, and have been playing with layer styles a
good deal, I have used these before, but only recently discovered the powerful possibilities hidden in 'Contour'
and 'Texture' under the 'Bevel' menu.  Using a combination of these Layer Styles to enhance the model I did this:

Stage 1
I began, thanks to a fantastic day out while I was at college videoing steam trains, with an image of the metal
plate front of a lock box at an old train station:
Now as you can see this isn't straight and it's darker on
one side than on the other… but both these things can
be fixed.
First I used the perspective transform tool in PhotoShop.

And to use this tool you need to first select the entire
image by using the Rectangular marquee tool to draw
around it, thus selecting it:.
Then select the Perspective Transform Tool, selecting it from the Edit/Transform/Perspective menu:
If you find this option greyed out, then most probably the image
is not selected using the Rectangular marquee.
If you find that Transform Perspective doesn't quite complete the
job, you can tweak it with the Transform/Warp tool:
While I was doing this I decided to crop the image as well, to select just the nicest part of it for my texture:
This also meant I didn't have to clone over the lock or the hinges
or the bevelled edges of the box (although liking the colour and
texture along the bottom I decided to clone over the lock after all,
it only took one click.)
Now to remove the difference in light and dark on the image, I just
created a new layer and used a gradient, picking colour from the
dark side of the image for the background colour and from the
lighter side for the foreground colour.
After this use of the gradient, the bend on the plate in each corner
becomes a little more obvious, so some cloning is necessary to
remove it, resulting in this:
Now that stage one is completed, I have a texture that
will be useful in more than just this one UV Map.  
And I can go on from this point and tile it if I need to
do so.
End of Stage 1
Brick Texture Tut
Rock N Roll Tut
Layer Styles Tutorial, Making a Texture with PhotoShop.
(if you already have a texture you want to use for this, you can go directly to Stage 2, if not, continue with stage 1 below.)
without increasing the polys on the model.      
Adding Structural Detail Using A Texture
"Metal Plate Fixed"
If you like you can now download the final fixed version
of this texture, below.  A ReadMe is included in the zip.
To go from this
to this