Most of us hear this question repeatedly, my response was always, our brain is used to patterns, but even if you answered this question with god, we only push the question a step back then who created god?
Lawrence Krauss, http://www.youtube.com/watch?v=7ImvlS8PLIo ,
you might have already :)
Gives us something to think about, and we can understand it a bit better, I find this argument the hardest to deal with, how anything could just be there? without a beginning.