When you say a poor conductor but not an insulator, I assume you mean something on the border between insulator and conductor.
Even an insulator is considered a conductor if electricity can pass through it. The rubber coating on wire can conduct electricity if a high enough potential exists between the wire and an exterior object. This tends to happen if you are holding the wires of a piezo starter when you push the button, for example, and can be used to make shock pens.
Air is a conductor in high enough voltages, which is how lightning can travel all the way between the clouds and the ground, while passing through a massive insulator.
I would say that if you are looking for relatively poor conductors, though, a good bet would be something like a semiconductor like graphite or silicon, or perhaps a metal like lead or mercury with poor conductivity.