Also know as full-contact twists (and you can add plates to the end of the bar which you are holding):
Grasshoppers:
In a push-up position, bring your left leg under your body and twisting at the hips, touch your left ankle to your right wrist.Return to the push-up position and switch sides, touching your right ankle to your left wrist.
With a kettlebell, pass the bell around your body in a clockwise direction, switching the bell from your right hand to your left as it comes behind your body and then from your left hand to your right as the bell passes in front of your body.After a dozen passes, switch directions and go counter-clockwise.I forget the name of these.
With a medicine ball held in both hands, bring the ball up to your right ear and swing it diagonally across your body until it reaches your left hip.After the desired number of reps, switch sides and go from your left ear to your right hip.These are called woodchoppers.
You can also buy or make an implement called a tornado ball.This is basically a light medicine ball attached to a short length of rope or cord.You can do chops or smashes laterally agaisnt a wall or overhead to the floor.
If you want to go old school, look into buying yourself a sledgehammer.I got an 18ib sledge for $35 at Home Depot.You can do all manner of swings against a large tire to build up rotational power.