First, peel the ginger root (or knuckle or ball or whatever innuendo you'd prefer to use; I'm partial to "fist"). The best way to do this is but cutting off the bits (or thumbs or bulbs or testicles--you know I like my innuendo subtle) and peeling them separately with a vegetable peeler, then peeling the bigger pieces.
Then wrap in a few layers of plastic wrap and foil. Label and freeze. Voila!
It's crazy easy to unwrap and grate a little of the frozen nugget into whatever I'm cooking. But consider yourself warned! After holding a frozen nub of ginger and going to town on a microplane grater for a few moments, your thumb will start to numb with the cold.
Lucky you, I've devised a handy cheat-sheet to save you from injury: