It depends on weather and what it was originally filled at -- you need to use a tire gauge to tell Just kidding!
I have an '02 (same as '03) and I keep mine at 42 front 40 rear. The Bridgestone tires that are standard on it will take a maximum of 50 psi so this is not too high. You get much better mileage at 42/40 versus the suggested pressure on the door plate.
The Toyota reccomendation was 35 psi front 33 rear, just as it is now.
Some drivers (myself included) use somewhat higher psi, primarily for tire life and balanced tread wear. This remains a somewhat controversial topic.
Never exceed the max cold psi spec on the tire sidewall; if you do, the responsibiity is yours. In a 2001 Prius, I now have tires that max at 44 psi. They do very well at 41F/39R. I expect them to last at least 55k miles.
Everyone ought to have a tire gauge and use it at least monthly! At least before road trips, check the funny little spare tire (60 psi) too.