widely used references for engineers in the helicopter industry:

Aerodynamics of the Helicopter; Gessow & Myers; hardcover; 1999

Rotary-Wing Aerodynamics; W. Z. Stepniewski, C. N. Keys; paperback; 1984

Helicopter Performance, Stability, and Control; R.W. Prouty; hardcover; 1995

More Helicopter Aerodynamics; R.W. Prouty; paperback; re-published 1999

Even More Helicopter Aerodynamics; R.W. Prouty; paperback; 1993

Helicopter Theory; Wayne Johnson; paperback; 1994

Other helicopter texts:

Military Helicopter Design Technology; R.W. Prouty; hardcover; 1998
Basic Helicopter Aerodynamics (AIAA Education Series); J. Seddon; hardcover; 1990
Basic Helicopter Handbook; paperback; 1995
Foundations of Helicopter Flight; Simon Newman; paperback; 1994
Helicopter Design and Data Manual; Stanley J. Dzik; paperback; 1984
Helicopter Flight Dynamics: The Theory and Application of Flying Qualities and Simulation Modeling (AIAA Education Series); Gareth D. Padfield; hardcover; 1996
Helicopter Performance (Matrix Series in Mechanical and Aeronautical Engineering); Donald M. Layton; hardcover; 1984
Principles of Helicopter Flight;Walter J. Wagtendonk; Hardcover; published 1996
Rotary Wing Structural Dynamics and Aeroelasticity (AIAA Education Series); R. Bielawa; hardcover; 1992
Rotary Wing Flight; paperback; 1940
Rotary Wing Conceptual Design Process Atlanta Ga; paperback; 1989

Books about specific helicopters & computer game strategy:

The McDonnell Douglas OH-6A Helicopter; Donald J. Porter; paperback; 1990
Mil 24 Hind in Action; Hans-Heiri Stapfer; paperback; 1989
Werewolf vs. Comanche: The Official Strategy Guide (Prima's Secrets of the Games); Tom Basham; paperback; 1995
Gunship: 82 Challenging New Adventures; Dave Prochnow; paperback; 1998

Helicopter History & Novels:

Black Hawk Down: A Story of Modern War; Mark Bowden; hardcover; 1999
Close Air Support: Armed Helicopters & Ground Attack Aircraft; Michael J. H. Taylor, Ray Hutchins; hardcover; 1996
Firebirds: The Best First-Person Account of Helicopter Combat in Vietnam Ever Written; Chuck Carlock; hardcover; 1996 (paperback; 1997)
Igor Sikorsky: Father of the Helicopter (Masters of Invention); Steven Otfinski; library binding; 1993
USMC Vietnam Helicopter Pilots; hardcover; 1995
Ceremonies of the Horsemen; Mark Staggs; paperback; 1997
Bonnie-Sue: A Marine Corps Helicopter Squadron in Vietnam; Marion F. Sturkey; hardcover; 1996 (paperback; 1996)
Hovering: The History of the Whirly-Girls: International Women Helicopter Pilots; Henry M. Holden; hardcover; 1994 (paperback; 1994)
Military Helicopter Doctrines of the Major Powers, 1945-1992: Making Decisions About Air-Land Warfare; M. Allen; hardcover; 1993
Paladin Zero Six: A Desert Storm Memoir by a 101st Airborne Attack Helicopter Company Commander; Rafael J. Garcia, Jr; Paperback; 1994
Primer of the Helicopter War; Charles Holley, Mike Slonkier; hardcover; 1997
United States Naval Aviation Patches: Aircraft/Attack Squadrons/Helicopter Squadrons; M. Roberts; hardcover; 1995
Vertical Challenge: The Hiller Aircraft Story; Jay P. Spenser; hardcover; 1992
Whirlybirds: A History of the U.S. Helicopter Pioneers; Jay P. Spenser; hardcover; 1998

Recommended for young readers:

The Boy Who Would Be a Helicopter; Vivian Cussin Paley, et al; hardcover; 1990 (paperback; 1991)
Budgie, The Little Helicopter; Sarah, Duchess of York; school & library binding; 1989 (paperback; 1996)
Helicopter (Take It Apart); Chris Oxlade, Mike Grey; library binding; 1997 (paperback; 1997)
Thomas and the Helicopter Rescue: A Revolving Picture Book With Flaps; Christopher Awdry, Owain Bell; hardcover; 1995
Working Hard With the Rescue Helicopter (Tonka Truck Storybooks); Cynthia Benjamin, Steven James Petruccio; hardcover; 1997

Helicopter Piloting / Maintence / Training:

Basic Helicopter Handbook (FAA Reprints Series); paperback; 1978
Commercial Pilot Test Guide: 1993-1995 for FAA-T-8080-16B Written Test/Questions, Answers and Explanations for Commercial Airplane, Helicopter, Gyro; paperback; 1993
Helicopter Maintenance (Aviation Technician Training Course, EE-HF-2); Joseph Schafer; Paperback; 1986
Helicopter Maintenance Study Guide; Schafer; paperback; 1981
Helicopter written test guide air regulations section; Andre S Rossin-Arthiat; spiral-bound; 1998
Instructor's Guide to Helicopter Flight Maneuvers; Knight; paperback; 1984
Instrument Rating for Airplane and Helicopter: Practical Test Standards (FAA-S-8081-4A); paperback; 1988
Personnel Safety in Helicopter Operations: Heli-rescue Manual; Robert Stoffel, Patrick Lavalla; paperback; 1988
Private Pilot Test Prep: Study & Prepare for Recreational & Private Airplane, Helicopter, Gyroplane, Glider, Free Balloon & Airship Certificates; paperback; 1995
Student Guide to Helicopter Flight Maneuvers; Knight; paperback; 1940

VHS Videos:

Apache: Attack Helicopter; 1991
Budgie, The Little Helicopter; animated; 1997
Grand Canyon National Park - Helicopter Exploration; 1994
Helicopter Gunships; Vietnam Home Movie; 1994
Heli-Kids: Helicopter Adventure for Kids (ages 3-9); 1995
Helicopter Safe Pilot Series; 1992
Helicopter Tech; 1998
Let's Go Fly a Helicopter; 1998
There Goes a Helicopter; 1995