The two arguments the apostle Paul gives for the existence of God in Romans are valid and relevant as well.
"For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse." Rom 1:20
"..in that they show the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them." Rom 2:15
While articulated by many, one popular reading of the argument from conscience is in C.S. Lewis book
Mere Christianity. He expounds the argument that universal Laws of right and wrong imply a Lawgiver in the first six chapter of the book. In his book, "The Abolition of Man"[
Abolition of Man Chapter 1,
Abolition of Man Chapter 2,
Abolition of Man Chapter 3 ], he tackles the subject of how education develops ones sense of morality. While doing so he provides various proofs of the doctrine of objective value, the idea that certain attitudes are really true, and others really false... Lewis calls this objective value the
"Tao". The two books go together.