I would be more than happy to second Firn's recommendation of Wages of Destruction. I think that it was the first book that challenged my beliefs about the motivations driving the major players. I'd always looked at the politics of the period through an exclusively moral (and somewhat awestruck) eye, but Tooze significantly altered my perspective to one far more focused on the economic reality. I'm not entirely sure why, but understanding the economic and social pressures of the era made it all somewhat more relatable.

I'm currently reading (and enjoying) Four Ball, One Tracer by Roelf van Heerden and Andrew Hudson. It's a great book, well written and edited. I get a little bit uncomfortable when an author badmouths other individuals (deservedly or not - I find it a little cringeworthy when the other parties have no recourse to defend themselves) but it's an important element in understanding the dynamics of EO at the pointy end of the spear. I'm not yet finished, but right now I'd recommend it. I'd really like to read Eeben Barlow's EO book, but it doesn't appear to be available on Kindle and the actual books are somewhat out of my price range.