Metals are characterised by having specular highlights that are a similar colour to the diffuse colour.
Good metals I usually reduce the diffuse intensity to say 0.5 and let diffuse and specular add up to one. Play with the glossiness for how rough the surface is… Lower values = bigger but softer specular highlights.
Use an environment map or raytrace some reflections (if it’s in a scene that has something to reflect of course)
Use a photo of some metal (even if applied at the wrong scale) it’ll give some decent variations of colour to add some interest and make things feel better…(plenty can be found for free at cgtextures.com) Given what I said earlier map it to diffuse colour and specular colour! (and maybe ray colour too if you’re raytracing reflections!)
If you are uing ray tracing then use a fresnel value too it adds a great depth to the material.