Here is a great exercise for MMA and many other sports that require rotational power. Want to improve you punching power, this should do the trick. Its a standing medicine ball toss to the side.
Here is another medicine ball exercise peformed by Ross from Rosstraining.com. This one is very specific to boxing and is guaranteed to increase you punch power.
here is another RossTraining.com video that should give you alot of ideas to put in your workouts. At 2:45 in there is an exercise using bands that will put some KO power into your hook. AWESOME!!!