This is just another method of adding the same type of border and creating an action for it at the same time. It keeps the original image dimensions (so don't crop too tight) , although you cant customise different sides as shown by oldfart. It might look long-winded, but it's not....it's very, very simple!
1.Open the image you want to add your border to.
2. If the actions palette isn't open do so by hitting alt+F9
3. Click the "Create New Action" button at the bottom (shown by red dot below)
4. In the box, give your action a title and set a shortcut key (I just set it to F2), and click the record
button (everything you now do will be recorded until you stop it)
5. Most of this is now going to be done using the default short cut keys.
6. Press D to reset the colour palette to black and white.
7. Press X to set white as the foreground colour
8. Press Ctrl+A to put a selection around the whole image.
9. Select Edit>Stroke and in the box that opens, set size to 11 pixels (you don't even have to select it, as its already selected) and make
sure Inside is checked in Location and click OK.
10. Press X to set Black as the foreground colour
11. Select Edit>Stroke again and set the size to 10 and click OK.
12. Press Ctrl+D to deselect
13. Press the "Stop Recording" button in the Actions Palette.
Finished! Now every time you want a border all you have to do is press the F2 key! Try it!