It depends on which model you are looking at.
Early 2003 (before April/May 2003) SR5's and Sports have gray cladding all around the bottom of the car. Early Sports also have silver-painted door handles, front grille and rear license plate garnish. Later 2003's have painted cladding that came in a package. For the SR5 it included: painted lower cladding, front and rear bumpers and rear license plate garnish, standard black running boards, fog lights and 16" 6-spoke alloy wheels. For the Sport Edition it included: painted lower cladding, front and rear bumpers, door handles, grille and rear license plate garnish and standard black running boards. Early 2003 V8's have a weight-carrying hitch while later 2003's have a weight-distributing hitch. There were also some color changes during the mid-2003 change, Natural White, which was originally unavailable on Sports was made available and they took out Imperial Jade Mica (dark green) and Impulse Red Pearl (red).
Basic changes in 2004 include a standard tire pressure monitoring system and the gauges are illuminated once you start the engine (vs 2003 where they only turn on when you turn on the headlights). SR5 models no longer have a telescoping steering wheel. There is an option for the third-row seats on SR5's and Limiteds.
That's all that I can think of right now. Hope it helps you out.