[Coda]

Amtgard RECOMMENDS a penny but you can use a nickel if you want. A dime is too small and a quarter is probably going to be too big.

That's actually the same selection of ranged weapons Amtgard has (for player classes, that is), but you can have rocks shaped like daggers if you want. :P Sadly, you cannot shape a rock like a convincing shuriken without leaving it with points too small for the rules. I tried. :(

That said... there are some monsters that have boulders, which are like giant rocks that deal double damage to armor.

Edit: On my field, actually, the most popular throwing weapon was actually a hockey puck. :P (Well, technically it was foam padding wrapped in electrical tape, but it looked like a hockey puck and complied with all the rules.)