Hard Landing, I forgot who wrote it but it is an excellent book. It is about the US airline industry during deregulation. Even if you are not interested in Commercial Aviation it is so well writen that you will not be able to put it down.
The best book that Prof Doganis wrote - in my opinion - was Flying off Course (ISBN: 0043870058 - Paperback - List Price: $18.95 Publisher: Routledge)
He also wrote Airline Business in the 21st Century (ISBN: 0415208831 - Paperback - List Price: $29.99; Publisher: Routledge) which to my mind was just and updated and revised version of Flying Off Course which focuses more on the economics of low cost carriers such as Go and Ryanair.
Another book to go for is Straight and Level - Practical Airline Economics by Stephen Holloway (ISBN: 0291398480).
The book Cellidh suggested is an excellent one. Airline Business... is fairly upto date and it touches on most aspects of the airline industry- including the hot trend in airlines forming alliances amongst themselves.