I have no conceivable qualification for writing this blogpost. I am by profession a philosopher and have precisely no theological training at all. What's more I have no particular spiritual standing to advise others on how to resist the wiles of the Enemy. It's all I can do to beg for the grace to manage that for myself. However, I have read a fair amount on this topic. This is partly due to an adolescent morbid period that I never quite managed to leave behind, and partly due to a wish to find just one good book that would help me know enough to battle spiritually without becoming unhealthily preoccupied. Here then are the results of my on-again, off-again researches.
Fr John J. Nicola's book is often referred to, and indeed he served as a technical adviser to William Peter Blatty et al. when they produced The Exorcist. I have never yet seen a copy of this book and haven't read it; so while many people quote it, I cannot really comment on it.
Malachi Martin was a fascinating character and a member of a brilliant but eccentric family. Various claims have surfaced over the years about his precise canonical status after he publicly parted ways with the Society of Jesus and what ecclesiastical recognition his activities as an exorcist had. I can't offer any clarification on these issues. What I can say is that Hostage to the Devil is a well written thriller with a somewhat spiritual twist. Martin claimed that these cases were real - which they may well have been - but he presents them as a novelist would rather than for spiritual edification. This book is more for the Stephen King fan than the serious Catholic.
Thomas B Allen is an author and journalist who is also a graduate from a Jesuit college. He researched the real incidents that gave Blatty his raw material for The Exorcist and produced a text entitled Possessed. It's a straightforward and readable account of certain strange events in the life of a boy in Maryland and the ultimate resolution of his sufferings in St. Louis, Missouri. It's not an overtly Catholic work but it does extend the benefit of the doubt to the Jesuits priests who genuinely believed that their patient was suffering demonic possession. A good book in its way but not a great one.
Then we have some books that are worth reading. Firstly we have Fr Gabriele Amorth's An Exorcist Tells His Story and An Exorcist More Stories. These books are serious about the reality of demonic action in the world and the Enemy's implacable hatred of God and the human race He created & redeemed. So far, so good. However, his style is a bit over-heated and some of his anecdotes are a bit ... well, strange. He has the authority of a great deal of experience behind him but his work is a bit thin on the theology of angels, fallen angels and their capacities for action. Read one or the other (if you've read one effectively you've read both!) but don't rely on Amorth alone.
Much better to go to Cristiani instead! Msgr Léon Cristiani's Evidence of Satan in the Modern World is sober, balanced and has a good grasp of the theology underlying this whole topic. It is particularly fascinating to read of the satanic activity surrounding the apparitions at Lourdes; I simply never knew that there were false visionaries after Bernadette met the Lady at the Grotto. Cristiani shows very well why we would do well to fear the devil but also why Christ's victory over him is never in doubt. The only flaw with this text is that the translation is a bit uneven and stumbles over various faux amis.
In the same vein as Cristiani but much more recent is Interview with an Exorcist by Fr Jose Antonio Fortea. It's not always an easy read but it repays the attention given to it. It combines practical insight with a solid doctrinal grounding. It's a clear one-stop-shop for the Christian who wants to know what the Church teaches without stirring up an excessive or morbid curiosity. With the exchange rate from Sterling to Euro being what it is right now, I'd say get your copy today.
Lastly, there is a book that comes highly recommended. It's called The Rite: The Making of a Modern Exorcist by Matt Baglio. Fr Basil Cole OP thinks it's "a wake-up call. It smashes the many myths created by Hollywood movies and other amateurs on the subject about exorcism and the role of the exorcist in the Catholic Church." I haven't read it myself but I'm familiar enough with Fr Cole's work to know that he's a sensible and sagacious critic. So it's probably worth a read.
Amended on 4 March 2010 to add:
A few months after I posted this informal review of the available literature, I read Baglio's book and can wholeheartedly recommend it. It's a simple and sincere narrative of a priest training in and practising exorcism as a part of his pastoral ministry, at the request of his bishop. It's calm, balanced and even-handed, and well worth reading.