Iconic or most recognizable to your everyday Joe Shmoe?
If its a modern icon (according to shooters) you're after then Glock (like it or not) or some other striker fired pistol like the Springfield XD line is probably the winner.
If its simply the most recognizable to the public it would have to be something like a Desert Eagle or S&W 500. I would also throw the good ol' 1911 in there, everyone knows what they look like. Like others in this thread have said the 1911 will never die.
Just my $0.02