During gameplay when you are walking around in any of the parks enter codes to unlock the effect you want.

Unlock ALL Mini-Games:
Press Square, Circle, Triangle, Square, Circle, Triangle, Right.

Unlock ALL Missions:
Press Square, Circle, Triangle, Square, Circle, Triangle, Square.

Unlock ALL Parks:
Press Square, Circle, Triangle, Square, Circle, Triangle, Square.

Unlock ALL Rides:
Press Square, Circle, Triangle, Square, Circle, Triangle, Triangle.

Unlock Extra $50,000:
Press Square, Circle, Triangle, Square, Circle, Triangle, X.

Unlock Extra 500 Thrill Points:
Press Circle, Square, Triangle, Circle, Square, Triangle, Square.