The books Realistic Railroading with Toy Trains (posted by OddIsHeRU) was the first book I bought and it is what got me to thinking about getting into 3 rail trains, I've read the book a number of times and loved it, each time it gave me more and more inspiration. The second book was posted 1st by Greg Houser called the Realistic Modeling For Toy Trains - A Hi-Rail Guide - by Dennis Brennan. These two books and then seeing all that was available got me even more interested and about 98% sure that I wanted to just do 3 rail Scale.
Great topic and thread, thanks for starting it, there are a number of books on here that I've written down to start searching for.