Automatic batting aim:
Select rookie mode. Hold the Analog-stick slightly in any direction while batting and
the batting cursor will automatically follow the ball.

Harder throws:
While playing defense, immediately before the CPU catches the ball, press the
Analog-stick in the direction of the base you want to throw to and press A.

Hold the Analog-stick in the direction to throw before the ball gets to the fielder then
press A. This works about 90% of the time.

Bunting:
Press L to bunt.

More player creation points:
Create and save a custom player using all available ability points. Return into edit
mode and select the player that was just saved. More points will be available that can
be added to his existing abilities. 

Fireworks:
Hit a home run or grand slam with the home team in their stadium during a night
game.

Dream stadium:
Hit three homeruns into McCovey Cove at Pacific Bell Park. 

Better defense:
Place the game on a harder difficulty setting for an awesome defense - but prepare to
face a difficult team.