Pause the game, then press Down, Left, Up, Right, Down, Left, Up, Right.
To unlock level 8 (Huntington), go to the big gray ramp with a blue streak on the bottom that is in front of a wall. Go off the ramp, and do an air trick (e.g. Christ Air). If you hit the wall in the middle of the trick, you will land it perfectly and get full points.
Play as Master Ao
Get all keys, photos, and coins in both wings of the dream house with any character to unlock Master Ao, the ultimate skater (full vert, street, balance meter, plus every trick).