One that I'm currently enjoying, but is best read by dipping in and out of it (ideal for your Armitage Shanks' library) is: The Story of the Giro d'Italia, A Year by Year History of the Tour of Italy, Volume On: 1909-1970, by Bill and Carol McGann.
There's a lot of stuff crammed in and it's obviously been painstakingly researched, full of info about the race, the riders, the bikes and background about the history of Italy too. I was disappointed that there weren't more pictures in it though, it's a bit annoying when the author refers to interesting pictures he has and they aren't in the book!