As someone who's always been curious about religion, these have been my most enlightening reads
  1. The Bible
    Of course.
  2. God is not great by Christopher Hitchens
    One of my favorite critiques of religion
  3. The year of living Biblically by A.J. Jacobs
    A pretty easy and entertaining read, I learned some interesting things
  4. The Book: on the taboo against knowing who you are by Alan Watts
    My favorite book on Buddhism and Hinduism philosophy
  5. Zealot by Reza Aslan
    Scholarly protective on Jesus of Nazareth
  6. The Age of Reason by Thomas Paine
    The most blistering critique of religion I've seen (next to the writings of Christopher Hitchens)