One book i've listened to for spirituality is "Zen Mind, Beginner's Mind."
I cannot tell you how much i've gained from this book.
It is secular. There is no big sky buddies who will save you if you only prostrate.
It just talks about how change occurs constantly, and how we can find peace as we understand that fact. And how we cannot attach to our current understand of life, because it won't enable us to grow. Yet we need some approach to life. So our approaches need to be flexible.
I listen to it on tape. Peter Coyote narrates, and he does a fabulous job.
I also liked "Drinking: A Love Story".
Also, Pema Chodron writes very well.
These are Zen approaches, without the other-world.
I'm a spiritual person, in that i truly care about others, and feel the pain within myself and when others feel pain. And i don't want to contribute to that pain.
But i don't believe in 'karma', or any other force that evens things up when a person does wrong. I haven't seen evidence of that.
"The Demon Haunted World" is also great.