Since I'm currently reading quite a fair bit that is related to work, I'll just respond with the book that is my current "fun" reading that I engage in before I go to bed: Steven Erickson, Dust of Dreams (Book 9 in the Malazan Empire series, some of the best epic fantasy fiction that I have read in a long, long time).
Only five? Okay, here goes:
If you define "useful" as "fun" and "enjoyable" then these are on my list:
Probably the works by Canadian authors Lisa Grekul, Myrna Kostash, and Janice Kulyk Keefer because my research on texts by these authors has brought me into contact with them as people, and they are generous with their time and insights in ways that I would never have expected. Even when they disagree with the ways I read their texts, we can have fruitful discussions; the kind only possible with living authors!
An author; an independent communications consultant; a lady of leisure; a professional triathlete; the principal of my own independent Humanities Academy; a screen-writer; the owner-operator of my own pub/bookstore...so many options, so little time...