Play through Career Mode to unlock the following cars:

You can earn any medal in the Boxed In event - Unlock Ardent
You can earn any medal in the Rod Rage event - Unlock Demon
You can earn any medal in the Swift Justice event - Unlock Enforcer
You can earn any medal in the Short Stretch event - Unlock Guardian
You can earn any medal in the Tommygunner event - Unlock Hitman
You can earn any medal in the King of Bling event - Unlock Honcho
You can earn any medal in the No Parking event - Unlock Hookzilla
You can earn any medal in the Monster Mash event - Unlock Kodiak
You can earn any medal in the Heads Up event - Unlock Magnus
You can earn any medal in the Laps of Luxury event - Unlock Opulent
You can earn any medal in the Toll 'N' Thunder event - Unlock Outlaw
You can earn any medal in the Bayside Brawl event - Unlock Phantom
You can earn any medal in the Raging Bull event - Unlock Rampart
You can earn any medal in the Trail Breaker event - Unlock Roughneck
You can earn any medal in the Shore Leave event - Unlock Streamline
You can earn any medal in the Heads Up event - Unlock TEC
You can earn any medal in the Catch My Drift event - Unlock Vulcan
You can earn any medal in the Killer Curves event - Unlock Wraith
You can earn a Full Auto medal in the Armageddon event - Unlock Warlord