Cheat codes:

10x Trick Score Multiplier:
     During  gameplay,  pause  the game and: Hold L1 and press Square,
Circle, Circle, Up, Down, Down

+8 Mins. Of Extra Trick Time (Career Mode):
     During  gameplay,  pause  the game and: Hold L1 and press Square,
Up, Circle, X

Special Tricks Meter Always Full:
     During  gameplay,  pause  the  game  and: Hold L1 and press Left,
Down,  Triangle,  Circle, Up, Left, Triangle, Square. Re-enter code to
nullify it.

Unlimited Balance:
     During  gameplay,  pause  the game and: Hold L1 and press Square,
Left, Up, Right

Big Wheels Mode:
     During  gameplay,  pause  the  game  and: Hold L1 and press Down,
Circle, Circle, Down

Hard Mode (Divides All Trick Scores By 10):
     During  gameplay, pause the game and: Hold L1 and press Up, Down,
Up, Circle, Circle, Square

Display Special Grind Meter:
     During  gameplay,  pause  the  game  and: Hold L1 and press Left,
Circle, Square, Triangle, Square, Circle, X

Unlock Tony Hawk:
     Using any rider, beat the game with 2 Gold Medals and 30 Covers.

Unlock Grandma:
     Without letting the timer run out, Retry any Career Mode Level 10
times.

Unlock Warehouse Park:
     From  THPS  String  together  a  bunch  of  tricks that are worth
200,000 points or more. NOTE: You must do this without using any other
programmers cheats like, oh, say the Trick Score Multiplier.

Unlock Burnside Park:
     From  THPS  Use  all  8 riders to beat the game, each with 2 Gold
Medals and 30 Covers.

Unlock Grandma's Video:
     Use Grandma to place in any of the 2 competition levels.

Unlock Rider Videos:
     Use  the  rider  whose  video you want to unlock, and earn a Gold
Medal on both of the competition levels.

Unlock Bails Video:
     Use Tony Hawk on the competition levels to get any 2 Medals.

Mat Hoffman moves:

Superman seatgrab truck driver: Left, Left, Circle 
Decade air: Right, Right, Circle 
No Footed One Handed Candybar: Left, Right, Circle 
One Handed Swing Leg: Right, Right, Square 
Seat grind 180: Up, Down, Left, R1, Triangle