Cheat: No damage
Got to options, then Cheat Codes, then enter "ontheroad"

Unlockable: Chevy Cobalt SS
Win Unbeatable Street Racers tournament.

Unlockable: Gemballa F355
Win by Invitation Only tournament.

Unlockable: Hotmatch Chingon
Win Choppers Of America tournament.

Unlockable: Tokyo Police Car
Complete the entire Tokyo challenge.