I suggest:
A People For His Name: A History of Jehovah's Witnesses and An Evaluation by Tony Wills - used by Ray Franz & James Penton as source material
The Desolations of the Sanctuary by Emil & Otto Sadlack - the reaction of some sincere German Bible Students to Rutherford's reforms of Russell's organization
DEMONISM and the WATCH TOWER by Roy D. Goodrich - the only publicly available collection of some of Goodrich's writings.
Captives of a Concept (Anatomy of an Illusion) by Don Cameron - the key deception of Watchtower dogma
each of these are available through Amazon or Lulu.com at reasonable prices.