If you're a lucky owner of Illustrator CS2, you can create some great borders that can easily be used in Photoshop in a very scalable way. (If you don't have Illustrator, move on. There's nothing to see here.)
illustrator to photoshop
As we've done in many of the techniques, you'll start by pressing Command-J (PC: Control-J) to duplicate the Background layer. Then use the Image>Canvas Size command, or press Command-Option-C (PC: Control-Alt-C), to add 1 inch of canvas (with the Relative checkbox turned on) to both the width and height. Finally, press-and-hold the Command key (PC: Control key) and click on the Create a New Layer icon at the bottom of the layers palette to add a new layer below the copied Background layer. In this case, I clicked on the Foreground color swatch at the bottom of the Toolbox, chose a shade of gray, and pressed Option-Delete (PC: Alt-Backspace) to fill this new layer with gray. I did this because my photo had a very light background and I wanted to see the edges of the image. (Depending on the image, you can also fill the new layer with white, if you choose.)
In Illustrator, use the Pen tool (P) to create a horizontal path that's approximately the width of your image. If you're not sure, guess, because you'll be able to scale the object in Photoshop. Select the path and copy it to the Clipboard (Command-C [PC: Control-C]).
Switch back to your Photoshop document and make sure that the copied Background layer is active. Press D to set your Foreground color to black. Choose Edit>Paste and select Shape Layer in the resulting Paste dialog. (If you forget to set your Foreground color to black before you paste, just double-click on the Shape layer thumbnail to open the Color Picker.) If the Shape layer is not the right size, press Command-T (PC: Control-T) and use Free Transform to change it to the appropriate size.
Repeat this operation for all sides of your image, experimenting with different brushes in Illustrator to create horizontal and vertical borders.
Here's the finished product. I pressed Command-Delete (PC: Control-Backspace) to change the underlying layer (Layer 2) to white. Then I clicked on the Add a Layer Style icon (at the bottom of the Layers palette) and added a soft, offset drop shadow to the photo layer (Layer 1).
If you want a bit more flexibility in editing the Illustrator shapes, choose Smart Object when you Paste in Photoshop. This creates a live link from Photoshop back to the original Illustrator artwork. Just double-click on the Smart Object icon in the Layers palette to edit the artwork in Illustrator. When you save and close the Illustrator document and return to Photoshop, the artwork will update (while preserving the position and scale of the pasted border).