The first Transcendental argument I am going to give is the moral one. William Lane Craig and Greg Bahnsen use this form of argumentation and I have been greatly influenced by both of these men on issues pertaining to arguments for God's existence. So here goes my formulation of the Transcendental argument for God's existence from what I will call "moral facts". Here it goes:
P1: If God does not exist moral facts do not exist
P2: Moral facts exist
C: Hence, God exist
What I mean by moral facts is that there are good and bad things independent of our recognition of it. This is sort of like the fact that sea world exists, even if no one recognized the existence of such a place as sea world the place would still exist. Likewise, with moral facts they exist independent of our recognition of it. Suppose there were a possible world P* where everyone thought that the holocaust was morally praiseworthy and that everyone thought putting your first born child into a microwave was morally obligatory, in P* everyone would be moral wrong in doing these things even if not a single human being recognized it.
God and Moral Facts:
If God does not exist then these sort of moral facts do not exist. God is a necessarily good being that always commands what ought to be done and what ought not to be done. It is necessary that God command the good in the Christian theistic tradition. This sort of God would be the necessary meta-ethical foundation for all moral facts.
No Moral Facts without God:
If God does not exist how could moral facts exist? They simply cannot. Some might argue for atheistic moral realism, the view that immaterial forms or propositions are our meta-ethical foundation for moral facts. But this view is implausible for a number of reasons: 1) It is hard to conceive of a immaterial objects having content apart from a mind with thoughts that possess content, 2) We are only obligated to persons and morality requires moral obligation and there can be no moral obligation on atheistic moral realism since they reject the person hood of God, 3) we would have no way to know what is in fact good because these immaterial forms or propositions do not cause or relate to the world, 4) The meta-ethical foundation of the good (forms or propositions) would be themselves not good because only persons can possess moral properties of goodness and badness. The good would not be good in this case which would be a contradiction.
The God of Christianity or tradition theism fulfills criteria 1-4 and thus if one wants to be a) reasonable and b) believe in moral facts then they ought to believe in the existence of God.