Pendulums are divination tools, used to answer yes/no questions and to assist in providing direction.  They work by responding to your subconscious mind.
 
Lepidolite
Associated with 3rd eye chakra
Lepidolite naturally contains lithium making it an emotional balancer.  It aids in gaining an emotional detachment to gain a greater perspective on a situation, and helps develop psychic abilities.  It also is known to help with anxiety and stress.  This stone would be useful for questions where it's a bit harder to detach from the situation, providing that healthy balance for a truer reading on the problem.
 
This listing is for 1 pendulum to be intuitively chosen by me.