There's a demon under every rock, around every corner, lurking in every dark alley, and in your closet! MUHahahaha! *Ahem.* So...
What are your Big 5 books on spiritual warfare?
These would be books on the theology and practical reality of demons, demon possession and oppression, or stories about people dealing with these issues. These can be books that deal primarily with sin or prayer, spiritual "armor," etc, as long as they have a significant "warfare" component. There are a lot of kooky books and authors out there, but there are some really good ones too. Go!