Last year I got in with doing baseball pictures of a local high school and I've been asked to do them again this year....do you have any ideas of any good poses for high school age baseball players?

I don't know that you potograph them much different than youth.  I have done them both with the traditional ready to bat pose or holding their glove.  I don't know if I'm that boring, but I find when you offer too many options, people seem to get more picky.  Someone else may have a better idea, but that is my 2 cents

 Have them lean against the fence, or holding the bat behind their neck with their wrists hanging over the bat.  You could even have them face the fence with their forearms resting on the fence, with a mitt on their hand (if the fence is short enough).  Have them "squat" on the base with a mitt on one of their hands and a ball in the other.  Have them toss the ball up in the air....just try different things that aren't the "normal" sports shots.

 Have them look through the fence!