Motion blur mode 

Press Up, Left, Circle, Down, Right, Square, Up, Down, Left, Right, Circle, Square at the main menu to unlock "Motion Blur" in options menu

Alternate paint job

Press Down, Square, Down, R1, Right(2), Up, Left, Circle(2), L2, L1 at the main menu. This will change the paintjob of your car when you begin a game

Unlock The Geeze Car

Collect all the coins in Rome Level 1

Unlock the P-Nut car

collect all the coins in Rome Level 2

Unlock the Froggy Car

Collect all the coins in Rome Level 3

Unlock Super Genius Car

Collect all the coins in London Level 1

Unlock the Turtle Car

Collect all the coins in London Level 2

Unlock the Ricochet Car

Collect all the coins in London Level 3

Unlock Fang Car

Collect all the coins in London level 4

Unlock Road Shark car

Collect all the coins in London Level 5

Unlock Portabello car

Collect all the coins in Tokyo Level 1

Unlock Street Eagle Car

Collect all the coins in Tokyo Level 2

Unlock Black Widow Car

Collect all the coins in Tokyo Level 3

 

Many of the cars you unlock more than resemble real car models... Here's a list of the cars that resemble real cars

Turtle car = VW Beetle Convertible

Ricochet car = Audi TT

Fang car = Mazda MR2 Spyder

Road Shark car = Honda S2000

Portabello car = Lotus Elise

Street Eagle car = Porsche 911

Black Widow car = Plymouth Prowler