Recommended Reading for Ghost Enthusiasts

Paranormal Investigation Techniques & Best Practices
Auerbach, Loyd.  A Paranormal Casebook: Ghost Hunting in the New Millennium. (2005) 
Auerbach, Loyd.  Ghost Hunting: How to Investigate the Paranormal. (2003)
Cornell, Tony.  Investigating the Paranormal. (2006)
Parsons, Steven.  Ghostology: The Art of the Ghost Hunter. (2015) 

History of Ghost Investigation
Ghost Hunting at the Psi-Encyclopedia (SPR) 
Price, Harry.  Confessions of a Ghost-hunter. (1974) 
Rogo, D. Scott.  In search of the unknown: The odyssey of a psychical investigator. (1973)
Rogo. D. Scott.  Phantoms: Experiences and Investigations. (1976)

Poltergeists
"Poltergeist" at the Psi-Encyclopedia (SPR)
Roll, William G.  The Poltergeist. (1972, 2004)
Rogo, D. Scott.  On the Track of the Poltergeist. (1986)