well besides sounding better, difference in the rear would be
the oval tailpipes replacing the quad ones..
front the front, if i am not wrong i think only the headlights have
a darker tint..
here's a pic, hope this helps 
oh thx man didn't notice the tailpipes before u mentioned it.
pretty obvious now haha. this means that i've seen a few S already
without realising they are S lol.
