When it comes to family and friends I prefer to be a little more controversial. I don't say any of the following in a mean way, they are just jokes. I don't give anyone too hard of a time because they were after all just being polite. I also realize that most people that say god bless you aren't even aware of the words they are saying; it's probably more of an obligatory remark as uncontrollable as a sneeze to anyone raised to be polite. The main reason I don't just say gesundheit or thanks and ignore the topic is specifically because people aren't aware of what they are saying. If you are just robotically repeating something that you don't even believe is it really politeness? The majority of people that say god bless you don't actually think that god is going to take time out of his busy schedule and perform a miraculous exorcism of the offending dust particle in my nose. So if they don't believe it, why say it? There are many ways to be polite regarding sneezes with out invoking the power of a god. For some generic things to say from various languages and some general info check out this wiki article. http://en.wikipedia.org/wiki/Sneeze
Here are some phrases I have said to friends and family when they say "(god) bless you" to me after I sneeze.
Are you sure you are qualified to wield that kind of power? I'm going to have to see your license.
Woh, careful with that, I'm allergic.
Ahhhh, it burns! (Followed by me running around and flailing about�)
Don't you think god has more important things to worry about?
Can I re-gift? I'd rather one of the starving kids in the world have his blessing.
Can I choose which god? I like Loki, he's funny.
No thanks, but thanks for the offer.
Thanks, but I'm full. I had a big breakfast.
Things I say when someone else sneezes. I try to avoid the awkward silence following a sneeze by replacing it with an awkward religious comment.
Our Father, who art in heaven, bless this child for he hath sinned against you. Cast out the evil spirit and protect him from evil (sometimes said in the kneeling position or at least with my head bowed down and my hands clasped; always said very dramatically and serious.)
God bleeee… god bleeee… god bleeee…hmm, god won't let me say it.
My authority having been revoked I must instead only wish you good health.
Bob (or dog) bless you.
High five! (Insert Borat voice here)
Ewww, you got your soul on me.
God damn you! Oh wait, is that how you are supposed to say it? I get so confused by your human customs.
That's really all the ones I'll say, or at least versions of those. I don't get up in arms about this or anything so don't take this as an angry atheist post. It's really all in fun. It doesn't even end at the god part, as I think it's funny that we say anything at all. So the next time you are around a sneeze whether it be your own or someone else's consider having a little fun with it. Don't be afraid to step out of the societal mold.