The only codes I know of for Jet Moto can only be used *after* you've beat a season with all the tracks on the hardest setting.
But if you want them, they are:

Super Agility: down,O,left,L1,left,right,left,right. (this lets you pull tricks quick and easy)
Zero Resistance: square,L1,triangle,right,L1,down,R2,triangle
Double Stunt Points: right,up,O,L2,triangle,O,R1,R2 (the name says it all)
Show off camera enabled: triangle,down,square,triangle,L1,L1,R1,R1 (this really sucks,try it)
Air Brakes: R1,R2,right,L2,up,O,up,O (very handy avoiding air wrecks)
Rocket Racer-triangle,up,up,L2,L2,up,up,up (makes you run turbo
speed all the time,you'll be winning cypruss track by 30 seconds with the right racer,it rocks!!!)
Unlimited Turbos: triangle,O,right,R2,up,square,up,triangle
(not much use but for acceleration with rocket code)
Ice Racing: up,R2,R1,right,L1,square,right,right (makes everything slippery as ice,very hard)