Medicine ball slams, Tire flips , Sledgehammer on the tire (when your doing this one make sure your in your fighting stance and when you swing the sledgehammer pivot like you're throwing a cross don't forget to turn your hips as well) , Gennady Golovkin uses kettle bells, he puts it on a flat surface and twists it to the right with his left hand and to the left with his right hand.
Cleans are a great athletic exercise. Not so much for punching power but they get you in shape and can show you where your weaknesses are.
it's not so much the exercise as much as how it is done. plyometrics are essentially loading a spring in the muscles and then releasing the spring. are you looking for start power to initiate the movement, or are you looking for reactive power with repetitions? ex. the exercise is medicine ball chest pass with a partner: start power: catch the ball and pause at the bottom (loaded) part of the movement to make sure you're not using momentum, then execute explosively reactive power: catch the ball with extended arms, riding with the movement of the ball towards your chest, loading the "spring", then pressing back against the ball's force just before you hit bottom. repeat 3 to 10 times (higher reps for power endurance) heavier (68% 1RM) barbell style exercises are good to train the muscle to fire as many motor units as possible. then go to start power (like above), then reactive power. get as many as possible to fire then get them firing faster.
BoxinScience has good advice in his post. If you want to do weights, I like cleans and other Olympic lifts (if you have access to good coaching). Done properly, you'll get stronger and add explosiveness without adding a ton of mass or sacrificing flexibility. It'll take time to see dividends, but it's worth it IMO. Watch out that you don't compromise flexibility and bulk up too much. Usually when I see guys focusing too much on the "big three" barbell lifts- deadlift, squat, and bench press- that comes at a price, and while it makes you stronger, it won't translate near as much to your punching power as you'd think. They have their uses, but I'd be wary of making them the cornerstone of your plan. I also prefer dumbbell and kettlebell exercises to using the straight bar. You'll lift less weight, but you'll get a better functional workout because your stabilizing muscles have to be engaged much more.
Hitting the heavybag alone makes me stronger, but less flexible. I can't imagine lifting weights. For me, learning about Joe Louis punching technique increased my punching power way more than any weight lifting could ever do. So much of punching depends on form and technique, not the size of your muscles. A simple change in the way you handle your balance when punching, or developing a shoulder snap, can instantly produce so much more power. It would be a shame for someone to not recognize that, and spend loads of time inefficiently developing power in other ways.
Lol having a big bench, squat, and deadlift lasts for about a minute in the ring. After that your either on an even playing field or outright ****ed.
Obviously hitting the heavy bag. I used to do loads of powerlifting, had a pretty good total in competition too. It doesn't do anything much for punching power though.