The Armstrong book is definitely a keeper. When I was in college many moons ago we had to read another Armstrong book for Civil Engineering transportation majors: The Railroad-What It Is, What It Does. A more in-depth study of why railroads do what they do.
Back to the topic, another book I like is Thomas Klimoski’s Building The Right-Sized Layout. Don’t let the subtitle about building a switching layout fool you. There are many great ideas that apply to any layout in this book.