2004 has the most dramatic changes. It has the new updated face, more standard options, new rims, LED brake lights with adaptive braking, Bixenons have adaptive feature (they move side to side following the curves), 6 speed manual tranny, have SMG option, have ZHP option... er, all I can think of off the top of my head.
I think around 2002, the only real change was the maintenance warranty got extended from 3yrs/36K to 4yrs/50K.
The sport package got clear turn signals somewhere before 2003.