Hidden Pitch
Using Ramon Martinez of the Boston Red Sox, use the 4th pitch key ('S' on the keyboard), even though he only has three pitches listed. He will throw a sadistic curveball at 107 MPH, every time. I do not think this affects his fatigue any more than your average fastball. This only works in League play.
Programmer Baseball Cards
If you press "S", the batter will spit. If you continue to press it, you will eventually see the the cards.