among other things...

Viewpoint points to fifteen reasons that it's far more rational to believe in God than to disbelieve:

1. The exquisite fine-tuning of the cosmic parameters, forces and constants.
2. The existence in the biosphere of specified complexity (i.e. biological information).
3. The fact of human consciousness.
4. Our sense that we are obligated to act morally.
5. Our belief in human dignity.
6. Our belief in human worth.
7. Our belief in human rights.
8. Our desire for justice for others.
9. Our need for meaning and purpose in life.
10. Our longing for life beyond death.
11. Our sense that we have an enduring self.
12. Our sense that we are free to make genuine choices and that the future is not determined.
13. Our sense that the universe must have had a cause and that it didn't cause itself.
14. Our sense of guilt.
15. Our sense that reason is trustworthy.

...and if you already believe, these articles are also good.

update: Theosebes reports on both the irrational and rational. One relevant quote from the rational:

Director of the Human Genome Project Dr. Francis Collins reflects on his spiritual journey from atheism to belief: "I had always assumed that faith was based on purely emotional and irrational arguments, and was astounded to discover, initially in the writings of the Oxford scholar C.S. Lewis and subsequently from many other sources, that one could build a very strong case for the plausibility of the existence of God on purely rational grounds. My earlier atheist's assertion that "I know there is no God" emerged as the least defensible. As the British writer G.K. Chesterton famously remarked, "Atheism is the most daring of all dogmas, for it is the assertion of a universal negative."

But reason alone cannot prove the existence of God. Faith is reason plus revelation, and the revelation part requires one to think with the spirit as well as with the mind. You have to hear the music, not just read the notes on the page. Ultimately, a leap of faith is required.

For me, that leap came in my 27th year, after a search to learn more about God's character led me to the person of Jesus Christ. Here was a person with remarkably strong historical evidence of his life, who made astounding statements about loving your neighbor, and whose claims about being God's son seemed to demand a decision about whether he was deluded or the real thing. After resisting for nearly two years, I found it impossible to go on living in such a state of uncertainty, and I became a follower of Jesus."