Do you ever have doubts about God's existence? What would it take to completely convince you?

To the Israelites the glory of the LORD looked like a consuming fire on top of the mountain. 

~Exodus 24:17

I don't think I have ever had doubts about God's existence.  I have grown up and lived in a Christian family where my dad's occupation is a pastor of a church.  I think because of that I have always believed myself to be a Christian all my life.  I believe that it wasn't until I had reached college when I had realized how important my faith was to me.  So after that point, I had persued into praying more and following and reading His Word more whenever I get the chance.