Under Extras on the main menu you can enter the cheat menu and enter the following codes:

Password - Effect

MYPRECIOUS - All Boards unlocked
GOINGDOWN - All Leaf SLide stages unlocked
WATCHAMOVIE - Unlocks all videos
TINYBUTSTRONG - Unlocks Arnold
THELEGEND - Unlocks Big Z
SURPRISEGUEST - Unlocks Elliot
SLOWANDSTEADY - Unlocks Geek
KOBAYASHI - Unlocks Kobayashi
IMTHEBEST - Unlocks Tank Evans

Note: These codes do not effect achievements.