Although technically a Christian, I consider myself spiritual. It's funny how faith is faith, and is something you do without proof, because it was only when I stopped looking that I was given the proof. I went atheist, or at least agnostic, for a few years. I have manic depression, and at that age I didn't even know that, but obviously the idea of believing in a loving God seemed absurd. I did, however, take a philosophical interest in other religions, and read up on some of them, even tried partaking in rituals and such. Eventually I came across Qi Gong, which used a form of meditation, and essentially one time I meditated, something strange happened, but after the experience I felt touched by something of a higher order, I believed in God again almost instantly, became pacifist, was quite an experience! Although after all this, I still believe your moral code is what sets you apart, what makes you worthy in God's eyes, why would he care whether you believe in him or worship him, so long as you value life and the feelings of other people, I'm sure he'll be happy.
Oh, and please don't use Descartes, he was such a dreadful philosopher, with his bloody triangle and silly arguments to prove God's existance. I'll tell you one of his arguments because it will make you laugh. Imagine someone comes up to you, and offers you a choice between two things in his hands. In one hand, a real ?50 note, and in the other, an imaginary one, which would you pick? The real one! Because the real one is better, because you can spend it. Real is better than imaginary. Now he would move on to defining God, whether you believe in it or not, after all, if you don't believe in something, you must define what it is you don't believe in! We would sum up that God is a perfect being that created the Universe, that is what we do or don't believe in. Now we go back to the note, real is better than imaginary, and since God is perfect, he must always have the best option in order to be perfect, and since real is better than imaginary, he must be real...stupid or what?