Actually, I had trouble figuring out what to say that's non-offending when someone sneezes. I ended up picking "Gazuntite", which means health (pls. don't ask why I need to say anything at all).
Also, there is a hilarious south park episode that delves into this issue. Here's a clip for some yucks: http://www.southparkstudios.com/clips/230805/science-help-us