Dry Erase White Board Marker (Pack of three $10)
This is the best tool ever when it comes to 3D Animation, you just draw on the screen and then when you are finished with what you draw on the screen with a dry cloth and your monitor is not harmed in anyway.
What you can use it for;
. To Plan out Arcs on different parts of the body.
. To Trace limbs, to figure out problems I.e. popping, moving in the wrong direction or to a specific place you need them to go.
. To Push the poses by drawing over the top of the existing pose in Maya.
. To Figure out how much spacing you have or what spacing you want to have.
. To Make notes on the screen, when you are watching it play through.
. To Trace the outline to check out the silhouette.
If you are worried about your screen being marked for the rest of it's life then you can put a clear sheet of plastic over the screen and tape in place. But it doesn't mostly leave any marks. :D