The ipod touch screen has a layer of quarts that should protect it from any scratches to the surface, but should you be worried about scratching it you can always get the clear shield scratch protection from ShieldZone.
Applying it can be a bit tricky, but the product comes with a link to an online video that shows you exactly how to apply it. Well worth the money if you want to give the ipod touch that extra protection without changing the way it looks.

Protective sleeves for Apple ipod touch