To unlock all skaters go to the main menu and press LB, LT, RB, RT, Down, Down, X, Y. If you enter it correctly, a message will popup.
To never end your skating career, while playing press Up, Up, Down, B, Up, X, Up, Right, A, A, X, B.
To unlock all clothing items on the d-pad, press Up, Down, Left, Right, X, RB, Y, LB.
All Freeskate Levels
At main menu put in RB, LB, RT, RT, Y, X, B, A.