"Religion presupposes the existance of a god/creator. Can anybody produce one piece of scientific (or otherwise) evidence that such a thing/being exists?"

Look for a First Cause. What created the universe? The Big Bang? What was there before the Big Bang? How to explain a universe created out of nothing without some recourse to a First Cause? I don't mean some guy with a flowing beard sitting on a cloud listening to harp music. Just an explanation for why there is 'something' rather than 'nothing'.