How Do I Know That God Exists?

In one of my Philosophy classes, we're reading Rene Descartes' meditations on philosophy. Right now, we're on meditation #3, in which Descartes attempts to prove through sheer logic that God exists. In my opinion, he failed. I don't doubt his conclusion; I fully believe that God exists. I just think that the logic Descartes uses to come to that conclusion doesn't make any sense. But could I do any better? What sort of logic would I use to prove the existence of God? Or, in other words, how do I know that God is real?

Of course, there's faith. We could simply believe that He exists, but that's not proof, or even strong evidence. We can put forth a better argument than "You've just got to believe it."

The existence of the earth could be strong evidence. It's so well balanced, it hardly seems like it could be random. However, if there were an infinite number of planets with randomly generated traits, there would have to be some life-sustaining planets among them. And besides, as Descartes might argue, this whole world could be an elaborate illusion. Even so, someone would have had to create this illusion.

I think that the strongest reason I have to believe in God (beside the Utterly Ridiculous and Admittedly Untrue Theory I hatched over five years ago) is the feelings I get in my heart. In the Gospel, we know that as the witness of the Spirit, but in a philosophical sense, it's empirical evidence; it just uses a sense that's not one of the traditional five senses. It's an inner sense, like introspection. I feel in my heart that God is real, and while I won't win any arguments citing that as evidence, I'm the only person that I really need to convince.

Maybe I can't argue for God's existence much better than Descartes did, but I know He is real, and I thankfully don't have to rely on Descartes' convoluted logic to come to that conclusion.