First was Osprey Elite #136: World War II Airborne Warfare Tactics which I found especially interesting as it discussed not only the concept generally, but the specific differences between the forces of several nations including Italy and Japan who weren't exactly known for the use of paratroopers.
Second was Osprey New Vanguard #8: Matilda Infantry Tank 1938 – 45. I recall having had a model of this vehicle in my youth; reading about it now, underpowered and undergunned, was something of a revelation. Fair read, moderately technical.