Various Cheats:
Pause the game,hold shift and type:

s66s = fat tire
4awd = Perfect Balance
4w62 = Add 8 minutes to run
648w = Unlock Burnside
648d = Unlock Warehouse
648a = Unlock School
as86wa84 = Always Full Special
466wss = Score X 10
ssw664 = Score / 10

Best Bike:
On both competition levels get gold medals to get the rider's best bike

Get THPS Burnside Level:
Use all characters to get all 30 covers and 2 gold medals

Get Tony Hawk:
Use any character to get all 30 covers and 2 gold medals

Get Neversoft Video:
Use Tony Hawk to get a gold medal on both competition levels

Get Grandma Video:
Use Grandma to win any medal in both competition levels

Body Front Flip:
With Rick Thorne press down , right , and trick button 1 (the one that makes you do flips and tailwhips if you changed your settings) and you will do a body front flip, works on PS also

Double TailWhip:
With Cory Nastazio press down , right , trick button 1 to do a double tailwhip

Double TailWhip 2:
With DMC press down , right , trick button 1 to do a double tailwhip