In the U.S. "Bless you" is common. When "God bless you" is used, it is said quickly, almost as a single word, g'BLESHu. In my experience (Northeastern US) "Gesundheit!" is actually QUITE common. That is probably regional, and it is probably from Yiddish rather than German. It is, incidentally, a tradition that goes back to the 1300s, because a sudden sneeze was often the very first symptom of bubonic plague.

If I sneeze, you say 'Bless you!' and then I say 'Thank you!'

In a more-or-less real-life situation Johnny Depp reacts to a sneeze in the audience at about 0:08. This is a good example of how "God bless you" is pronounced in the U.S. And then he adds "Or 'gesundheit,' whichever you prefer." https://www.youtube.com/watch?v=D5CbW7_j0s0

== American English == The other person says "God bless you!" or "Bless you!" and then you say "Thank you." or "Thanks."