I'm not sure if its been mentioned in previous posts (can't see it) but my favourite by far is "10,000 Hours" by the late Peter Corley-Smith. It details the author's career as a commercial helicopter pilot in Canada in the pioneering days of the late 50's through to his retirement in the 70's, flying the Bell 47. Corley-Smith flew Stirlings in WWII as well but this gets scant mention. This book captures the 'romance' of being a commercial helicopter pilot brilliantly. Corley-Smith's education in a different era is obvious in his use of the english language (How many books have you read recently which feature the word 'Stevedore'.) and his writing style is very readable. Highly recommended.
The author of "Low Level Hell", Hugh Mills, is still going strong and is an occasional poster on the "Helikitnews" forum/discussion group.