Two books recommended by other members here that I have read are
"Sapiens" nonfiction
"Sophie's World" fiction
Other books I have read, and can off hand recommend are
"The Handmaid's Tale"
"Brave New World"
"Elmer Gantry"
All three above are fiction.
If you are in a behavioral science field you may also want to read
"Stigma"
I have attempted to read "A History of God" by Karen Armstrong. The book is very encyclopedic and was tough for me to read. I heavily endorse "The Sins of Scripture" by John Shelby Spong, retired Episcopal bishop of Newark, NJ. I, also, found "Man's Search for Meaning" by Viktor Frankl 'non-religious' and speaks to me from the mystical side of humanity.
Godless, by Dan Barker
God Delusion, by Richard Dawkins
God Delusion was really good. I appreciated the points were made in the simplest form. I will definately look for Godless.