Enter the following cheat codes as your name in Single Player mode:

Unlock all Tracks: Enter "BIGLEY"
Unlock all Cars: Enter "MECHANIC"
Turbo Mode: Enter "SKATES".
Stretchable Track: Enter "ELASTIC"
Stay in the air longer when you crash: Enter "LUNAR"
See only your wheels: Enter "JUSTFEET"
Race a long 40 laps: Enter "LONGLONG"
Overhead View: Enter "MINICARS"
Oulton Park Island Circuit: Enter ": DINKYBIT 
Oncoming Car Traffic: Enter "BANGBANG"
Lock Framerate During Qualification: Enter ": "TECHLOCK"
Instant damage when you touch rival car: Enter "DUBBED"
Faster Car: Enter "FASTBOY"
Bouncy Barriers: Enter "PADDED"
Bounce away from collisions: Enter "BCASTLE"
Blurry mode: Enter "CASTLETRIPPY" or "TRIPPY"
Stay in the championships: Enter "PUNCHY" 
(No matter how many points you score)