As well I added a basic example to show metallic shaders under some different lighting conditions, the one to the far left is chrome with color to black, the other two spheres are default grey and white.

As the diffuse value works as a multiplier of the color you will get the same result by setting the diffuse to black, this is what I wanted point out in my first post. Because other metals such as gold or copper are based on low diffuse values and colored specularity where they get most of their illumination from the specular highlight I added a blinn with a yellow color, a diffuse value of 0.2, and the specular color set to the same as the material color for the final sphere as we're on the topic. All polished metals can be made this way, it's simply a question of getting the color, reflectivity and specular highlight right to work with the ligthing conditions in your scene and to mimic the metal you're trying to make. If you leave the color at black, set the diffuse value high instead and keep the specular highlight at yellow you'll get a similar result in a case like this.

With something like a mirror, I think you'd want some more diffuse than in the case of chrome as mirrors come out quite bright even when there's very little light in the scene, again getting perfect looking mirror glass would be difficult and mental ray or maxwell materials would be much better suited in terms of something photorealistic.