If you enjoyed Signature in the Cell, the natural next question is a philosophical one: if the universe and life point beyond themselves, what kind of cause could account for them? Here are three books that take that question seriously. Two of them are classics you can read free online.
1. There Is a God by Antony Flew (with Roy Abraham Varghese)
My main recommendation. Antony Flew was one of the most influential atheist philosophers of the twentieth century. In 2004 he announced that he had changed his mind, and Stephen Meyer mentions this moment in the introduction to Signature in the Cell. In this short book Flew explains why. He walks through the questions that moved him: why the universe has laws at all, why it had a beginning, and how life and its coded information could arise from matter alone.
What makes it valuable is the attitude behind it. Flew follows his old rule of following the argument wherever it leads, even when it leads away from a position he defended for fifty years. It is not a religious book. Flew ends up at a philosophical belief in a Creator, not at any particular faith, which makes it a good bridge between the science in Meyer's book and the deeper philosophy of creation.
Best for: readers who want an honest, accessible account of how a careful philosopher reasons about where everything came from.
2. Natural Theology by William Paley (1802) - free
This is the book that made the design argument famous. Paley opens with his well-known watch: if you found a watch lying on a heath, you would conclude it had a maker, because its parts are arranged for a purpose. He then spends the rest of the book on the eye, the joints, the muscles and many other examples from nature, arguing that the same reasoning applies to them.
Darwin read Paley as a student and admired him, and much of the modern debate that Meyer joins is a reply to Paley in one way or another. Reading the original shows you where the argument started and lets you judge both Paley and his critics for yourself.
Read it free: Natural Theology on the Internet Archive (PDF, EPUB and plain text).
3. Confessions by St. Augustine, Books XI-XIII - free
Most people know the Confessions as an autobiography, but its last three books are among the deepest reflections on creation ever written. Augustine asks what God was doing before he made heaven and earth, and answers that time itself is part of creation, so there was no "before". He then works through the opening verses of Genesis, thinking about what it means for something to come into being out of nothing.
It is fifteen centuries old and still surprisingly modern. His thoughts on time are often compared with the idea in modern cosmology that time began with the universe.
Read it free: The Confessions of St. Augustine on Project Gutenberg (Pusey translation).
Where to start
If you only read one, read Flew's There Is a God. It is short, modern and connects directly to Signature in the Cell. If you want to go to the roots of the debate, Paley and Augustine are both free and well worth the time.