Look, I'd rather you not say "bless you." But it seems most of you aren't ready to take that leap, so here's Expedia's guide to politely responding to a sneeze in just about every country in the world. Mexico's is especially fun.
Below each continent's map, there are some extra tips and facts about the history of colonization - it turns out that sneezing etiquette roughly follows patterns of colonisation. Former British colonies tend to use "bless you," French colonies use "to your wishes," and Latin America follows the central European standard of "Health!"
Still no word on what to say after a sneeze in Vatican City.