I have become enamored with printing photographs on metal. This medium has a completely different look from any type of fiber, paper, wood surface that I've seen before. The lab I use, BayPhoto , prints on the surface of aluminum sheets. They use four different surfaces for this dye infusion process. Since the photo is infused on the exterior of the aluminum the depth of the colors and levels of gloss vary depending on the surface you choose for your print.
Check out their special print page http://www.bayphoto.com/metalprints/ for more details. If you desire to see the various surfaces the easiest way is to send them a photo and have them print a 3" x 5" image using the different surfaces. Then you'll be able to do a side by side compare on one image and make your choice.