"Oh my God" has always been my go-to phrase for expressing shock. But, seeing as I'm atheist, I think it's a bit silly to swear on a god that I don't believe in. So, I'd like to replace this phrase with a secular one. The problem is, alternatives like "Oh my goodness" don't have the same punch to them, and they sound like you don't want to say 'God' because you don't want to take his name in vain, instead of the real reason of not believing.
What are some good secular alternatives to this phrase, that aren't also weaker?