04 has the differences that everyone says:

-Change in styling... Front end and rear end in 04
-Performance is the same with the exception of the aerodynamics (better in 04) and slight upgrades like brake pads and and tranny in 03
-04 has A Centered Tach vs Center Speedo on the 03
-the green glow ring at the ignition in 03
-Heated seats, mirrors, and sunroof as factory options in 04 (Sedan only)
-3rd style for rims in 04 (5 solid star)
-STi available in 04
-Yellow available in 02-03 (2 shades)
-No yellow in 04
-Red that resembles Fire Red in 04
-Dark Red (almost burgundy) in 02-03
-04 has intergrated head rest in Front seats and all seats also have a different material than 02-03
-02-03 had slightly narrower seats compared to 04
-All black interior in 04 while 02-03 had black and blue
-Peter Solberg winning Drivers Championship

note: DO NOT get after market Brake pads without upgrading the Brake Rotors... The stock Rotors will get damaged if you get stronger/different Pads. This is a fact because I know someone that it happened to and he is a Mechanic at Subaru =)

There maybe a few more small things I've missed but these are a lot of small things.

Hope that helped.

:banana: :banana: