Andrew Boyle. Trenchard. London: Collins, 1962. Finally got around to buying a copy of the standard biography of a crucial figure in the early RAF.
L. E. O. Charlton. Charlton. Harmondsworth: Penguin, 1938. Charlton's autobiography, originally published in 1931 — so after his almost-resignation from the RAF over bombing in Iraq, but before he became a well-known airpower pundit. A nice blue Penguin paperback, still in the original dust-jacket.
Constantine FitzGibbon. London's Burning. London: MacDonald & Co., 1970. This popular account of the Blitz was recommended to me as a source on pre-war fears of bombing. I'm not sure how useful it will be, but it was very cheap — though still about 6 times the original $1.65 cover price!
Christopher Frayling. Things to Come. London: BFI Publishing, 1995. A little book about the big film of the even bigger book — how it came to be, Wells' intimate involvement in the whole production, and why everyone in the future wears tunics with those giant triangular things over the shoulders. (Well, that's what I want to know, anyway …)
Claude Grahame-White and Harry Harper. Air Power: Naval, Military, Commercial. London: Chapman & Hall, 1917. On the lessons of the Great War for the future of airpower, and how after the war Britain can and must exercise control over the air as it has over the sea.
F. W. Hirst. The Six Panics and Other Essays. London: Methuen, 1913. Hirst was the editor of the Economist. This is the only contemporary book I know of which discusses the airship panics (and then only in a single brief chapter). I've been looking for my own copy for years!
John Langdon-Davies. Air Raid: The Technique of Silent Approach, High Explosive, Panic. London: George Routledge & Sons, 1938. A journalist who had witnessed the air raids on Barcelona applies his first-hand knowledge to the British case. He seems quite critical of the government's ARP literature.