What are Porter's Five Forces?

Dr. Michael Porter, a Harvard professor, identified five elements that can be used to analyze the competitive forces in an industry ... now expanded to include a sixth force.  These six forces are ...
  1. Rivalry among the firms in an industry
  2. Threat of entry by new competition
  3. Threat of substitute products
  4. Bargaining power of customers
  5. Bargaining power of suppliers
  6. Bargaining power of complementors