In some company, I'll say "bless you" out of habit. For those who wondered, I have heard that the reason people started saying that is because your heart stops very quickly when you sneeze, so something about saving your soul from Satan in case it doesn't start up again? Silly Christians...
At work (which is now where I usually am when someone around me sneezes - possibly because my workplace is full of allergens?), I often look to see where the person caught the sneeze. If in the elbow, I smile and nod with approval. If in a hand that they will then put on a keyboard that I will have to use later in the day, I sort of look at them funny, as if to suggest they should wash their hands. Or if I'm feeling bold, I might suggest that they use their elbow next time. If they don't even attempt to catch it, and just sneeze openly into the air, I will likely scowl at them. Although they are usually not looking at me, so they don't know that I did.