For those (and there are some) who think we have no proof either way, here is a sketch of a proof that God does not exist:
God, if existent, is omnipotent, omniscient, and morally perfect.
Omnipotent: God has the power to eliminate all evil.
Omniscient: God knows when evil exists.
Morally perfect: God has the desire to eliminate all evil.
Evil exists. (Earthquakes, war, famine, ... lots of bad things in the world)
So either God doesn’t have the power to eliminate all evil, or doesn’t know when evil exists, or doesn’t have the desire to eliminate all evil.
That is, God doesn’t exist.
This argument is certainly valid (the conclusion follows from the premises).
Is it sound? (Given its validity, are the premises all true)? ... Well, perhaps God is not all three of (all powerful), (all knowing) and (morally perfect). Perhaps there's an ignorant creator, an impotent Demiurge, or a big baddie. But otherwise, yes this is a sound argument (pace Leibniz and that best-of-all-possible schtick). So its conclusion is true.
There is no god.