Some people say that reading Richard Dawkins caused them to become atheist. For me, it was very clearly "Artificial Life" and the code I wrote playing around w/ "evolving" Corewars code.
I managed to eek out a little "evolution" in my experimentation. I was never particularly religious to begin with. My simulation code caused me to deeply consider the power of evolution. Here was this tiny change, evolved from randomness in a minuscule virtual "petri dish", out of a tiny amount of ingredients that were brittle and unforgiving of the slightest change, on a time scale that was the smallest fraction of a fraction of the age of the universe.
Observing the sheer magnitude of the chemical "parallel computing substrate" at the scale of atoms and molecules, interacting in real time, across a space as large as the Earth, in a timescale measuring billions of years, and over a wide variety of temperature and energy gradients made me aside any concerns that all life couldn't have arisen from randomness.
I didn't need an "intelligent designer" after that. Nature, the vastness of space, the minuteness of atoms, and the overwhelming scale of time were enough.