Play as 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 vamp. Use the ramp to grind onto the bullhorns, and jump into the small room to unlock Day Smith.

Play as 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 equals 20,000+ points to unlock Vanessa. You can manual in between tricks, as you don't have to do a 20,000 point single trick.

Play as Volcano
Successfully complete the game by completing all objectives with any rider to unlock Volcano.

Unlock Levels in Road Trip
To unlock levels in Road Trip, go to the Press Start screen and enter the codes listed below to unlock the corresponding levels:

Las Vegas: Y, R-Trigger, L, L-Trigger, Right, Y
LA: Y, Left, B, B, Left, Y
Chicago: Y, Up, B, Up, B, Y
New Orleans: Y, Down, Right, Up, Left, Y
Portland: Y, A, A, B, B, Y
Boston: Y, Up, Down, Down, Up, Y

Unlock New Outfits
Go to the Press Start screen and enter the codes listed below to unlock the corresponding outfits:

BMX: X, B, Left, Right, Left, X
Elvis: X, L-Trigger, L-Trigger, Up, Up

Two New Riders
To unlock riders, go to the Press Start screen and enter the codes listed below to unlock the corresponding rider:

The Mime: B, Left, Right, Left, Right, Left
Big Foot: B, Right, Up, Right, Up, Y

Unlock Tiki Battle
Go to the Press Start screen and enter this code to unlock the Tiki Battle: L-Trigger, L-Trigger, Down, R-Trigger, A, L-Trigger.

Unlock Videos
Go to the Press Start screen and enter the codes listed below:

Mat Hoffman: R-Trigger, Left, X, Left, X, Left, R-Trigger
Kevin Robinson: R-Trigger, A, B, Down, Up, R-Trigger
Cory Nastazio: R-Trigger, Y, X, X, Y, Y, Y, R-Trigger
Seth Kimbrough: R-Trigger, Up, Up, X, X, X, R-Trigger
Reuben Alcantara: R-Trigger, Left, Right, Left, Right, Left, Right, R-Trigger
Nate Wessel: R-Trigger, Down, B, X, Down, B, X, R-Trigger
Big Ramp: R-Trigger, Up, Down, Left, A, A, A, R-Trigger
Joe Kowalski: R-Trigger, Up, A, B, Down, R-Trigger
Rick Thorne: R-Trigger, L-Trigger, Right, R-Trigger, Left, R-Trigger
Simon Tabron: R-Trigger, L-Trigger, L-Trigger, R-Trigger, L-Trigger, L-Trigger, R-Trigger
Day: R-Trigger, X, Left, Left, Y, Right, Right, R-Trigger
Mike Escamilla: R-Trigger, X, A, A, X, A, A, R-Trigger

Unlock All Music Tracks
Go to the Press Start Screen and enter the following L, Left, Left, Right, Right, Right, A, A.

Unlock Kid's Bike
Go to the Press Start Screen and enter the following A, Left, Left, L, R, Left.