Chickenhawk and other good 'helicopters in action' books
my all time favourite bought for my xmas by one of my best mates, is Snake Pilot by Randy Zahn. Randy was at tiem fo wirting cheif pilot for ERA Helicopters in Alaska probably pre buyout/merger with Texair.
Another classic is Dustoff by the now late Michael Novostiel, the decorated WW2 bomber pilot and post war pilot and Air Force Reserve Lt Col who volunteered for Warrant Officer Candidate School /Army Flight School and went to Vietnam.