Faster Gameplay
At the team select screen, press L,R,L,R and then press L,A,Z,R,B,A,L,L

High Gravity
At the team select screen, press L,R,L,R then press Up,Down,L,Up,R

Low Gravity
At the team select screen, press L,R,L,R, then press Up,R,A,L

All Hits are Homeruns
At the team select screen press L,R,L,R, and then press L,A,C-Down,C-Right

All Players Ratings to 10
At the team select screen press L,R,L,R, then press B,A,R,B,A,L,L

Dedication message
When you see the MLB logo when you start up the game, press
C-Up, R, B, B quickly and you'll see the secret dedication message and hear a chime to confirm that you did it right.