The most fundamental of Hindu deities, is the Trinity of Brahma, Vishnu and Shiva - popular deities include Ganesha, Krishna, Hanuman and goddesses like Lakshmi, Durga,Saraswati.
Many lingas are covered by a metal sheath and given a face so that the lord is more accessible to his devotees. These are the mukhalingas. Some have the entire image of Shiva carved on the surface.
The Panchamukha linga shows five heads which represent the five elements.