First up is a work that presents the darker side of tea history, and yes Virginia, it's true - tea is not all frilly and dainty things and wondrous health benefits and all that rot. Like any other commodity that's worth a damn, it has a rather checkered past - and present, now that you mention it.
But it's the past that Roy Moxham deals with primarily in Tea: Addiction, Exploitation, and Empire. I haven't had a chance to read this one yet, but I gather that it covers some of the same territory as Empire of Tea, a quite worthwhile work which I have read and never miss an opportunity to plug.
On a distinctly lighter, and more fragrant, note is Diana Rosen's Chai: The Spice Tea of India. Rosen also brought us The Book of Green Tea, one of many books on this topic. Chai is a lot less likely to bring you down than Moxham's book as it takes a look at the history and background of this distinctive Indian drink, complete with beverage and food recipes that make liberal use of it. Thus far Tea Guy has found himself to be quite resistant to the alleged charms of chai, but that doesn't mean you have to be.
While we're on the topic of tea and spices and history and India and whatnot, why not take a look at Spice: The History of a Temptation, by Jack Turner?