Try the Sharpening Tool in Photoshop CS5

If you want to sharpen certain areas of an image while leaving the rest alone, try the new Selective Sharpening feature in Photoshop CS5. Instead of having to duplicate layers, then erase portions you don’t want to sharpen, just use the Sharpening tool (triangle). It’s better at preserving detail than the Smart Sharpen filter or other sharpening tools, and can even sharpen areas that are not in focus! It’s also brush-based, so you can use pressure sensitivity with a pen and tablet. For safety, duplicate the layer and use it there.