Stadium Passwords
On the matchup screen of a Preseason game, press SQUARE to go to Preseason Options. Press L1 to Toggle the Home Team as defaut stadium. Then scroll to the stadium you want to unlock (their text is red). Enter the following codes to unlock stadia:
Old Carolina: CAROL
Good Ol' Days: SEPIA TONE

Tiny Players
At the main menu, hold L1 + R1 and press Down(2), Up, Left(2), Right.

Bonus Stadiums
Enter one of the following passwords to unlock the corresponding home team stadium:

Stadium Password
2050 LIGHT YEAR
Galactic GOVT OWNED
Good Ol' Days SEPLA TONE
Old Carolina CAROL
Old Chicago WINDY CITY
Old Denver 5280 FEET
Old Detroit AUTOMOBILES
Unknown EMERALD