I don't believe in God or organized religion... or most other widely-accepted God alternatives.
However, I don't know enough to rule out Diesm and I still think there is a possibility that our (humans on Earth) version of God could be some long-gone alien race.
I believe the big bang is our most plausible account of our universe's history... but I don't know how you can believe in the big bang without thinking must be beyond that... and it is truly mind-fucking.
And not everyone is up for the mind-fuck and the toll it can take... so we created religion :)