Here are four core arguments against God's existence that have persisted since ancient times. Using these four arguments as an organizing principle, I present for your consideration the Four Renaissance Horsemen.
Lack of empirical evidence- Discovery trumps revelation. Heliocentrism challenged older notions of a Heaven above the earth and a Hell below. Bruno challenged the view of a universe created for mankind.
The argument from evil- The problem of evil is easily resolved by removing divine will from the equation. Montaigne understood that the world is only as good as we make it.
The argument from reasonable nonbelief- If the existence of the gods were self-evident, everyone would believe. The burden of proof is on religion. Galileo understood that credulity isn't a virtue.