One of my favorite effects for an image is the tilt-shift effect. It makes an ordinary image appear as though it is a miniature model, as the photo of Times Square in NY above shows. Tilt-Shift Photography has a great tutorial to show you how to turn your image into a tilt-shift masterpiece, using just the tools built-in to Photoshop. Keep in mind that you want to give the impression of a miniature model. Miniature models are usually viewed from above so try and choose a photo with an elevated viewpoint.