Chickenhawk by Robert Mason is possibly the best Vietnam/helo's in war book ever written. Would also recommend 'Night Dogs' by Kent Anderson - another Vietnam classic. The follow up is also excellent - 'Sympathy for the Devil'.
I've just finished 'Eight Lives Down' by Major Chris Hunter. The true story of a British bomb disposal expert in Iraq. Superb book and one very brave man.
It has recently been released in paperback too.
Eagle402