Hmm... What I liked about "Mankind's Search for God" was that it was very similar to the college Comparative Religion course I had taken just a couple years before -- before I quit college because Armageddon was coming and a worldly education would, of course, be of no value in God's new system of thiings (blah blah blah). It was almost scholarly, if you ignore the lead-me-to-the-jws bias.
The one I'm glad I kept, though, is the Kingdom Interlinear. It's handy to have the original Greek with the word for word translation, so you can draw your own conclusions compared to the NWT nonsense in the margins.
My favorite wt book experience was probably the extra NWT that I cut from its spine and shredded page by page.