PS2
There is a Cheats section under Options. Enter these in exactly and most will also work on the Xbox version!

Agro (Special Move For SUVs And Trucks)
dfens

Bunny Ears (On Motorbike Rider)
getheadl

Faster Pedestrians
urbansprawl

Flaming Head (On Motorbike Rider)
trythisathome

Increase Car Mass In Arcade
hyperagro

No Damage
ontheroad

Pumpkin Head (On Motorbike Rider)
getheadk

Smiley Face (On Motorbike Rider)
getheadj

Snowman Head (On Motorbike Rider)
getheadm

Unlocks More Areas
roadtrip

Zone (Special Move For Sport Bikes, Tuners And Exotics)
allin