Mind Overcoming its Cankers by Acharya Buddharakkhita is one of our most recommended books. It is a profound exposition of the āsavas, the mental pollutions that maintain samsāra, the endless wandering around, and thus the endless unsatisfactoriness.
Acharya Buddharakkhita does this by means of the Sabbasava Sutta, the second sutta of the Majjhima Nikaya (the middle length teachings of the Buddha) and the old Commentaries thereon.
Although the book may seem a bit dry and theoretical at first, it hides a deep practical manual for the Buddhist practitioner. For anyone practicing Buddhist meditation it is more than worthwhile.