Pendulums are divination tools, used to answer yes/no questions to assist in providing direction.  They work by responding to your subconscious mind.
 
Black Tourmaline
Associated with Root Chakra
Black Tourmaline is known as an excellent grounder and protector.  This would work especially well on questions surrounding security, protection, your foundations (in life) and how to place yourself in the best position regarding these issues.
 
This listing is for 1 pendulum intuitively chosen by me.