Lol.. I say it all the time.. don't give it one thought.. sometimes I say .. oh my stars.. or shit dam!!!
OMG= oh my gosh! But i use wow, incredible, well bugger me! To mix it up.
And the occasional shiver me timbers! When I'm feeling extra piratey
There are a lot of words for "god", gosh, Greasy Grimy Gopher Guts, goodness think of anything that begins with "G".
I still use OMG, Holy Shit and Jesus Christ. Old habits are hard to break. LOL.
I worked with a religious woman who used "OMW" for "oh my word" just so she didn't even hint at taking her God's name in vain — despite easily being able to mean "oh my goodness." I didn't mind so much untill one day she spoke "OMW" and it sounded so forced and unnecessary, and was an obvious display of "I don't even say 'OMG' because that's what a good Christian I am." It was one of the few time I saw her wear her religiosity on her sleeve.
So, I don't really have an equivalent phrase. I don't want to go out of my way to have secular terminology for casual expressions. On the other hand, I avoid this phrase — mostly because I think it makes me sound like a teenage girl.
Oh my F-ing god.
Here is one I like.
Now that one rolls off my tongue.