Enter the following codes at the 'Hit Start' screen. 

Code    -    Effect 

Down, X, X, X, R1, R1, R1 - Adrenaline meter always full
Down, Triangle, Triangle, X, X, R1, R1 -All riders have fiery hands and feet
Down, Up, Left, Down, Right, Down, Left, Up - Invisible bikes
Square, Right, Right, Triangle, Down, Square - Level Select (Free Ride) 
Down, Triangle, Circle, X, Square - No on-screen displays
Down, Up, Circle, Down, Up, Circle, Down, Up, Circle - Perfect balance
Circle, Triangle, Left, Right, Left, Circle - Unlock ''gear'' rags (rider options)
Circle, L1, L1, Up, Up - Unlock ''vegas'' rags (rider options)
Square, Right, Right, Triangle, Down, Square - Unlock all levels except in Road Trip
L1, L1, Down, R1, X, L1 - Unlock Tiki Battle mode
Triangle, Down, Left, Left, Down, Square. - Unlock Vanessa
Triangle, Right, Up, Right, Up, Square - Unlock Bigfoot
Triangle, Left, Right, Left, Right, Left - Unlock Mime
Triangle, Up, Up, X, Up, Up, X - Unlock Volcano 

Triangle, Up, Down, Up, Down, Square - Unlock Day Smith (Day will be hanging out in the OKC level. Find him and he will become available in both Session and 2 player modes) 

Circle, L1, L1, Up, Up - Unlock Elvis outfit for riders 
X, Left, Left, L1, R1, Left - Unlock Kid's street bike (for all riders): The bike is found in the Chicago level after you rescue the kid with the medi-vac chopper. 

Square, R1, Left, L1, Right, Square - Unlock Las Vegas in Road Trip mode
Square, Up, Down, Down, Up, Square - Unlock Boston in Road Trip mode
Square, Up, Triangle, Up, Triangle, Square - Unlock Chicago in Road Trip mode
Square, Down, Right, Up, Left, Square - Unlock New Orleans in Road Trip mode 
Square, Left, Triangle, Trianlge, Left, Square - Unlock Los Angeles in Road Trip mode 
Square, X, X, Triangle, Triangle, Square - Unlock Portland in Road Trip mode. 

L1, Left, Left, Right, Right, Right, X, X - Unlock all music tracks
R1, Up, Down, Left, X, X, X, R1 - Unlock ''Big Ramp'' video
R1, L1, Right, R1, Left, R1 - Rick Thorne FMV 
R1, Up, Up, Circle, Circle, Circle, R1 - Seth Kimbrough FMV 
R1, Circle, Left, Left, Square, Right, Right, R1 - Unlock ''Day Flatland'' video
R1, Square, Circle, Circle, Sqaure, Square, Square, R1 - Unlock all Cory Nastazio videos
R1, Up, X, Triangle, Down, R1 - Unlock all Joe Kowalski videos
R1, X, Triangle, Down, Up, R1 - Unlock all Kevin Robinson videos
R1, Left, Circle, Left, Circle, Left, R1 - Unlock all Mat Hoffman videos
R1, Circle, X, X, Circle, X, X, R1 - Unlock all Mike Escamilla videos
R1, Down, Triangle, Circle, Down, Triangle, Circle, R1 - Unlock all Nate Wessel videos
R1, L1, Right, R1, Left, R1 - Unlock all Rick Thorne videos
R1, Square, Circle, Circle, Square, Square, Square, R1 - Unlock Ruben Alcantara videos
R1, Up, Up, Circle, Circle, Circle, R1 - Unlock all Seth Kimbrough videos
R1, L1, L1, R1, L1, L1, R1 - Unlock all Simon Tabron videos. 
R1, Up, Down, Left, X, X, X, R1 - Unlock Big Ramp FMV. 

Unlock Volcano:
Beat the game by completing all of the objectives. 

Unlock Day Flatland Video:
Choose Session and select 2 minutes, then choose Day Smith and score at least 250,000 points. 

Unlock Mime: 
Complete every Gap. 

Unlock Vanessa In L.A.:
On top of the brick building you will see a girl sitting down. Do an adrenaline trick in front of her that worth 20,000+ points to unlock her. 

Unlock Day Smith In OK City:
Go up to the ramp that you put in place with the fork-lift and into the secret garage. Grind on the black box, and it will open up into a vert ramp. Use the ramp to grind onto the bullhorns, and jump into the small room. 

Unlock Bigfoot in Portland:
Get across the river and perform an adrenaline trick between the two kickers at the bottom of the hill. There is a camera between them. Bigfoot will appear.