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.

Unlockable: All Cities
To unlock all of the cities in the game, insert "ROADTRIP" (minus the quotes) in the in-game cheats menu.

Unlock Flag Vinyls
Find 12 Rockstar logos in Cruise Mode.

Cheat: Unlocks Atlanta & Detroit
At options menu, go to cheat codes. Enter roadtrip.