I like this Leibnizian cosmological argument for God's existence, as presented by William Lane Craig in The Future of Atheism: Alister McGrath and Daniel Dennett in Dialogue.
1. Anything that exists has an explanation of its existence, either in the necessity of its own nature or in an external cause.
2. If the universe has an explanation of its existence, that explanation is God.
3. The universe exists.
4. Therefore, the explanation of the existence of the universe is God.
A very fun argument! Fun, because of Premise 2. Craig writes:
"Premise (2) is, in effect, the contrapositive of the typical atheist response to Leibniz that on the atheistic worldview the universe simply exists as a brute contingent thing. Atheists typically assert that, there being no God, it is false that everything has an explanation of its existence, for the universe, in this case, just exists inexplicably. In affirming that if atheism is true, then the universe has no explanation of its existence, atheists are also affirming the logically equivalent claim that if the universe has an explanation of its existence, then atheism is not true, that is to say, God exists. Hence, most atheists are implicitly commited to (2)."
Premise (3) is, of course, obvious.
Premise (1) "merely requires any existing thing to have an explanation of its existence." What it does not allow is the idea that there could be things that just exist inexplicably. (1) states that there are two kinds of beings: viz., necessary beings and contingent beings.
Therefore, God exists.