Blender 3D: Noob to Pro/Every Material Known to Man/Mirrors
From Wikibooks, the open-content textbooks collection
Mirrors can add an extra level of realism and beauty to your work. They can be applied to any surface, flat or round.
To texture a mirror, keep all settings as default except:
Mirror Transp
Ray Mirror: On
RayMir: 0.7
Fresnel: 1
Fac: 1.17
Also, a how to here : http://youtube.com/watch?v=ZMW0jyUfnb4