Faster Clouds:
At the title screen, hold L1 + L2 + R1 + R2 & press Up.

Extra Jumping Power:
Upon finishing the game, go to stage select screen, flip through the levels until you see 'extra'. Restart the game & you'll be able to jump 5 times in a row instead of 3.

World Select:
At the title screen, highlight 'Game Start' & press Up, Up, Down, Down, X, X, Left, Right, Left, Right, X, Triangle, X, Triangle. When you start a game, press Right to select your world.