My favourite books as a practicing aviation Boffin:-
HELICOPTERS
Fundamentals of Helicopter flight, Simon Newman
Everything he's written, Ray Prouty
AERODYNAMICS
Aerodynamics, Clancy
DEALING WITH FOREIGNERS
Scientific Unit Conversion, Francois Cardarelli
PHILOSOPHY
Slide Rule, Neville Shute
New Science of Strong Materials, J E Gordon
STRUCTURAL ANALYSYS
Engineering Mechanics - Statics, Hibbeler
Formulae for Stress and Strain, Roarke
MECHANICS OF FLIGHT
Kermode
STABILITY AND CONTROL
Feedback and control systems, Schaum
Flying Qualities and Flight Testing of the Aeroplane, Darrol Stinton
DESIGN
Anatomy / Design of the Aeroplane, Stinton
Joint Aviation Requirements, JAR-VLA, Very Light Aeroplanes, JAA
OTHERS
All the Worlds Aircraft, Janes
An Engineering Data Book, Munday & Farrar
Best Pubs and Inns, AA
If you buy nothing else, buy Clancy and a set of Stintons. If you are involved in Helicopters and buy nothing else, Simon Newman's book, and the three volumes of "Helicopter Aerodynamics" published by Rotor and Wing International (Prouty).
Glad to hear of other peoples suggestions.
G