Profile, by Jason Barker.
Various articles from Watchman Fellowship, a Countercult organization.
Jehovah’s Witnesses: Their Claims, Doctrinal Changes, and Prophetic Speculation. What Does the Record Show?, by Edmund C. Gruss (Xulon Press).
Reasoning from the Scriptures with the Jehovah’s Witnesses, by Ron Rhodes (updated and expanded) (Harvest House).
Robert Bowman, Jr. has put together a research bibliography.