Unlockables:

Unlockable Cars and Drivers:

Jak 3
Have a Jak 3 save file on your memory card

Jak II
Have a Jak II save file on your memory card

Jak (Original)
Have a Jak and Daxter save file on your memory card

Daxter
Play for 5 hours then pay 50,000 Orbs in Secrets Shop

Kiera
Beat the game

Klever
Beat Beachfront Drive Circuit Race

Razer
Beat Northern Tour Ciruit Race

Sig
Beat Spargus City Death Race

UR-86
Beat Kras City Qualifier

G.T. Blitz
Beat the Game

Naughty Dog Car
Unlocked in the Secret Shop

Sand Shark Car
Unlocked in the Secret Shop

Pecker
Play for 10 Hours and pay 60,000 orbs in the Secret Shop

Unlockable Hero Mode:
1st, you have to get a Gold in every race. Then go to the secret shop, where you'll see hero mode available for 50,000 Orbs.