Stan Hansen's book 'The Last Outlaw' is probably the most comprehensive look at what it's like to be a gaijin wrestler in Japan, I'd definitely recommend that one - similarly, 'Masked Decisions' by The Destroyer is a great read as well with some good info on wrestling in the 60's and how wrestling got started in Japan. The Destroyer became something of a cultural icon over there and as far as I know there's no other English language book that touches on those pre-NJPW/AJPW days. Lou Thesz's book 'Hooker' is a must read for sure, there was a lot Lou didn't like about wrestling by the end of his career, but it's a great look at his philosophy of what wrestling should be. He also goes quite in-depth looking at the history of pro-wrestling in the US, which was certainly interesting. Gary Hart's 'My Life in Wrestling' is fantastic, he was one of the smartest men in the business and gives a very frank account of his life and career. Well worth hunting that one down. I'd probably put JJ's book in my top five as well, unless there's any I've forgotten.
A couple I'd mention as well, Billy Robinson's 'Physical Chess' has some great info on the British catch-as-catch-can style and Billy's time in Japan and then the AWA, but it's rather on the short side. 'The Cowboy and the Cross' by Bill Watts has a ton of info on Mid-South, as you'd expect, but is super preachy and Watts comes across as a bully and has a tendency to ramble on for pages about American football.