Well, these are typical of my bookshelf, plus a lifetime of reference books extremely useful for FT.
I rarely read non-fiction, and I have two very heavy books on the go at the moment, but both very useful.
One is the original 1957 Experiment in depth by P W Martin, and basically studies the theories and methods of Karl Jung, and how they can be used to seek enlightenment. It also contains some very sound psychological theories.
The second is a highly technical alien related book, The song of the greys, by Nigel Kerner. This has more technical twists than any other I've read, but after about 300 of 400 + pages, I can now say it presents the most logical theory of alien abduction I've read so far (and I've read most of them).