http://www.action-fx.com and more at http://www.adambaumann.com
There is another thread in here about sports photoshops, good place to get some ideas.
If you have more pictures with different poses that would make a huge difference, And the cut off of the "state championship" sign in the background is something that could really make a difference. I like what you are doing in the background with the images. Use more images like that for the background but make them bigger. Also the main images could be bigger and overlap. There is a lot of dead space. Also you need to try and make the images and the text work with each other, most of the time neglecting to do so will not make a sucessful poster. You can do this with color, size, location, accents, etc. Hope this can help.