How do you create mirrored features on a part?

I'd like to know the easiest way to create "mirrored" features on a part. For example, if I'm creating an extrusion on one side of a part how can I duplicate that exact same extrusion on the other side of the part WITHOUT having to manually re-create it. I'm sure there is a simple way to do this, I just don't know how. Any help is greatly appreciated.

SolidworksParts And Features