There are multiple "metallic" options on the market, and they differ in their final look, and quality. There are basically 4 options to get a "metallic" print.
Dye-sub aluminum
Metallic Photo Paper (kodak)
Coated inkjet metal
Metallic inkjet paper
The quality level of dye-sub aluminum varies greatly between vendors, but well done is spectacular. A pure mirror high gloss finish and a nice rigid piece of aluminum ... Bay Photo is one of the best. Supposedly they do it without "prepping" the aluminum, not sure if that's true but this processes basically gasses the special dyesub inks into the subsurface of the final material, leaving it perfectly smooth.
Kodak Metallic photo paper if properly mounted is also very good, with the same ultra smooth high gloss finish. It is a gorgeous look as well, but can only be produced using RA-4 processes. Despite all the talk about limited gamut photo papers as measure by profiles, the end result is rich saturation and gorgeous colors. The resulting print has some beautiful qualities depending on the colors - to me it achieves the most "metallic" look since it is a transparent emulsion allowing the silver metal base color to show through. Note that because it's a photo paper it may actually be less expensive to than printing your own inkjet prints on metal or metallic paper.
Coated inkjet (either metal or paper) varies even more in quality, but one problem with it is the ink is laying on top of the media. To rival the perfectly smooth finish of the other two requires some post processing coating, and personally I've never seen either that is quite as good, but I have seen some that are good. I've never seen a metallic inkjet paper that allows the metal quality to show through as well as the Kodak Metallic paper. However, these are the only viable options if you want to do it yourself.