Am I rebelling against my upbringing? My husband? And more interestingly, what do these options say about the people who use them?
There is certainly no reason to impart God's blessing upon a sneezing person; no longer does it mean they'll be dying of the plague, nor is it likely the person's soul has escaped through the sneeze. (We do, however, know that sneezes can travel up to 100mph, which might make 'Wow' apropos.)
Naturally, I asked my friends on Facebook, most of whom say 'God Bless You' or 'Bless You'. One of my friends replied, "Bless you. I'm an atheist and I don't speak German. lol." She might want to take up German, since 'Hesundheit' translates to a God-free 'good health', as does the Spanish, 'Salud'. (That one doesn't work quite as well for us, though, since we think of that as a toast.) Less popular but far fancier is the French 'à vos souhaits', or from one, simply, 'haits'. Almost no one who wasn't German replied with 'Gesundheit'.
My German sister-in-law surprised me by sharing that according to Knigge, the Deutsche Emily Post, you don't say anything. Emily Post (from her website, not the grave) has nothing to say on the matter. Miss Manners, on the other hand, was typically entertaining and seemed to support her Gentle Reader's annoyance that you have to say 'Bless you' every time someone sneezes, even if repeatedly. (The onus is then on the sneezer to graciously reply, thank you.)
It does make sense that the most proper response is nothing at all, and that it's the responsibility of the sneezer to simply say, '"Excuse me". But in this blessing-heavy world, silence would be seen as rude.
Etymology suggests that 'gesundheit' made its way into the American vernacular because the early-mid-century American thinkers wanted to separate themselves from God.
I asked my father about it. "You certainly didn't learn 'Bless you', from my family. That comes from your mother's side. Those Midwesterners will look for any excuse to bless someone."
Right. Moving forward, 'gesundheit' it is.