Just ordered a copy of this new book from Adam Gorightly: Saucers, Spooks and Kooks. Looks very good! Here's the theme of the book from the publisher:
"From flying saucer crashes to underground alien bases, a number of modern mythologies have come into being since the advent of the UFO era in the 1940s. But how much of these myths is real, versus being the invention of either government agencies or deluded conspiracy theorists? Saucers, Spooks and Kooks provides an eye-opening survey of the history behind these stories, and the individuals promoting them."