There is a conscience in man; therefore there is a God in heaven.
Every effect has a cause; there cannot be an infinite regress of finite causes; therefore, there must be an uncaused cause or necessary being; this being is God (The Cosmological Argument, proponents- Aquinas).
There is observable order or design in the world that cannot be attributed to the object itself; this observable order argues for an intelligent being who established this order; this being is God (The Teleological Argument, proponents- Aquinas).
All men possess a moral impulse or categorical (moral) imperative. Since this morality is not always rewarded in this life, there must be some basis or reason for moral behavior that is beyond this life. This implies the existence of immorality, ultimate judgment, and a God who establishes and supports morality by rewarding good and punishing evil (The Anthropological (Moral) Argument, proponents- Kant).
Man has an idea of an infinite and perfect being. Existence is a necessary part of perfection. (Therefore) an infinite and perfect being exists, since the very concept of perfection requires existence (The Ontological Argument, proponents- Anselm).
Every normal person is born with the idea of God implanted in his mind, though it is suppressed in unrighteousness (Rom. 1:18). As the child grows into adulthood, this idea becomes clearer. Critical experiences in the course of life may make this idea come alive (The Argument that God is an Innate Idea, proponents- Augustine, C. Hodge, Calvin).
All people believe that something is true. If God is the God of truth and the true God, then God is truth. This Truth (capital T) is the context for all other truth. Therefore the existence of truth implies the existence of Truth, which implies the existence of God (The Argument from Truth, proponents- Augustine, A. Strong).
Man is restless. He has a vague longing for blessedness. This longing was given by God, for man is restless until he rests in God. The presence of this longing is an indirect proof of God existence (The Argument from Blessedness, proponents- Augustine, Aquinas).