Rotor head and flybar
The fly bar, I think, ,ostly balances the main blades. They are on a single bar whose pitch alters with the cyclic, but not the collective (I think, lots of "I think"'s here!). The bar is supposed to be near-perfectly balanced otherwise it causes really nasty vibrations in the rest of the machine. Rememeber, this thing is a huge spinning top, really.