Go to the Enter Cheat Code screen and use the following codes to unlock cheats and extras. Some passwords were provided by the PS3 Major League Baseball 2K7 board.
Password - Effect
themick - Adds Mickey Mantle (Rating 100) to Free Agents.
Black Sox - Unlock all cheats, with the exception of Topps cheats.
Game On - Unlock all extras.
Derek Jeter - Unlock everything but the Topps baseball card cheats in My Cheats.
mightymick - Unlock the Mighty Mick Topps cheat.
triplecrown - Unlock the Triple Crown Topps cheat.
m4murder - Big Blast.
Power Hitting
To increase hitting power, insert "triplecrown" at the cheat code menu. If done correctly, the heart of your lineup (3rd, 4th, and 5th batters) will have increased hitting (50%). This will last for one game only.
Save money in Franchise mode
Release a high paid player to free agency, then offer them a new contract. Their asking price may be lower than what you were already paying them. This could save your team millions of dollars. However, sometimes your players will demand more money after you release them -- so make sure to save the game before attempting this.