One of my favorite special effect techniques is to mirror an image. It's one of the techniques I teach during the Photoshop workshop I conduct in my home, and I've used this idea for many different kinds of subjects. This one is a night shot of government buildings in London. The technique works best when there are diagonal lines, curves, and other unique graphic elements that, when mirrored, become something very different than they are in reality.
The technique is pretty simple. Open an image, copy it to the clipboard, and then use Image > canvas size. In the dialog box that opens, double the width of the picture and place the new area on the right side. Then use Edit > paste followed by Edit > transform > flip horizontal. Click on the move tool and move the floating layer in place such that it mirrors itself. You will now have a panorama format -- much wider than it is high. If you want to resize it (which is what I did here), use Image > image size.