Most solid materials are classified as insulators because they offer very large resistance to the flow of electric current. Metals are classified as conductors because their outer electrons are not tightly bound, but in most materials even the outermost electrons are so tightly bound that there is essentially zero electron flow through them with ordinary voltages. Some materials are particularly good insulators and can be characterized by their high resistivities:

Good Conductors 

Copper

Aluminum

Platinum

Gold

Silver

Water (salts)

People and Animals

Trees

Good Insulators 

Glass

Porcelain

Plastic

Rubber

Water (without salts)