“What in god’s name”
“oh god”
“for god’s sake”
Those (and more) are oft urged to be said under life’s common circumstances. But as an atheist who believes with a high degree of certainty that this ‘God’ person is nothing more than a figment of human imagination I feel a sense of guilt whenever I feel the urge. I sometimes replace ‘God’ with ‘Og’ but those outside the dope are unlikely to know who or what ‘og’ is.
So what are my alternatives, if any?
I usually go with
“What the fuck?”
“Oh shit”
“Jumpin’ Jesus on a pogo-stick!”
Frith
Watership dpwn
Watership Down
excuse me
Why do you feel guilty? 
Bob
“By Grabthar’s hammer!”
“By the Sons of Warvan!”
“A Elbereth Gilthoniel”
“Bob dammit!”
Yeah, I like that!
I second Tomm…'s “O Varda Starkindler” suggestion!
“By Aulë’s mithralloy guts” works for me, too.
There seem like a lot of obvious options if you don’t mind swearing. But if you want ones that you can say in front of your grandma, there’s always:
“What on earth”
“oh my”
“for pete’s sake”
I’m assuming you still want the meaning of the expressions to be understood . . . otherwise, you can pretty much say whatever you want.
What about Og?
I find that fuck works well for these situations.
What the fuck?
oh fuck,
for fuck’s sake.
The list goes on.
Holy Hannah!
Great Honk!
Dangit!
Oh my golly!
Holy moley!
Goodness gracious me!
Now guess which ones I actually use, and which I got from my kid’s Uncle Scrooge comic book. 
I used to know a guy that said “I swear to Rudy” all the time. Then there’s Bill Murrey’s “Mother Puss Bucket!”
Mine are more reseved problems like
“I am blessed” or “I am thankful” were I mean I have a lot to be appreciated but not to imply I have some hidden power to be thankful to, as it were.
I sometimes feel someone might feel better if I said “I’ll say a prayer for you” but I can’t in good concience.
I’ll never get why this makes people feel guilty. I dont believe in Santa Clause, but I wouldn’t have any trouble using his name in an expression.
I say “swear to god” “oh god” “pray to god” and all kinds of crap like that. I dont think it implies I believe anything in particular. And I dont think its hypocritical to say “thank god!” when something good just happened, even if I dont believe in god.
When a person says that, is he really praising his holy lord? Or is he just repeating an expression? I think it’s the latter.
Oh, and I always say “bless you” when someone sneezes. Because it’s polite, and not because I am excersising his demons or something.
What should we say when someone sneezes? “FUCK YOU!”?
Keep that pepper away from me!
You’re so good looking.
“Geizundheit!”
or,
“Tissue?”
I hate the way “Gezunheit” sounds. And I never have a tissue to offer.
Then how’bout “prosit?” Germans use it as a toast to health, but Scandinavians use it for sneezes. At least the ones I know do. Apparently it descends from the Latin, so it makes you sound clever too. 