Reason #1: Looking at the world and being disappointed.
Reason #2: Creation.
In a sense the debate about evolution vs. creation is, for me, supremely irrelevant, and completely fails to address the substantial problem of existence: origins. (Add to that that I'm just not all that interested in science.) Regardless of the age of the earth, of the adaptation and evolution of human kind, of my personal interpretation of the book of Genesis, evolution cannot explain the philosophical problem of the spark of existence.
How is it that something is here at all? Our knowledge of the "Big Bang" alone makes it very clear that something hasn't always been here, and I don't think belief in a designer is all that far-fetched when you consider the other options.
And then there is the astonishing, amazing unlikelihood of the universe. To provide you with a cliche, standing at the top of a mountain and surveying everything around me is something that, for me, minimises the possibility of chance by rather a lot. Seeing something of the order that governs even the smallest organisms. Watching a child grow. Wondering how such beauty could simply evolve of its own volition. Viewing by chance the raw power of nature and our own defencelessness. It's strange, given that my other reason to believe so far is a rejection of the reality of the (social) world as it is. The (natural) world, as it is, is so wonderful that I do not think it is possible without a Creator.
All this makes the following Bible verses really resonate with me:
For you created my inmost being;
you knit me together in my mother's womb.
I praise you because I am fearfully and wonderfully made;
your works are wonderful,
I know that full well. Psalm 139: 13-14
For since the creation of the world God's invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that men are without excuse. Romans 1:20
For these reasons, if I ever tried to be an atheist I would be a very bad one. I cannot get out of my head the sense that there is something too amazing here to be a fluke.
So far, I am aware that my reasons to believe lead only to belief in a God, identity unknown. The reasons I specifically chose to follow Christ will come soon.