In freestyle press and hold L2 while jumping and enter one of these codes and release L2.
Hart Attack:    Right, Left, Down, Up, Left
Cliffhanger:    Right, Left, Down, Up, Down
Aerial:         Left, Right
Double Cancan:  Left, Up, Right, Up, Left
Nacnac:         Left, Down, Right, Down, Left
Nacnac:         Right, Down, Left, Down, Right
Tailstand:      Down, Down
Front Fender Grab: Up, Up       

Slower Commentaries:
At main menu press Down, Up, Up, Right, Triangles, Square, R2.

Extra Game Modes:
At main menu press Square, Triangle, Circle, Circle, Up, Up, Left.

Thanks to Revolution reader ScOpE and Robin Daemen!