Try a Russian Kettlebell. ( http://www.russiankettlebells.com/ )
I use a 16Kg for Ju-Jitsu training and it is an awesome tool. I have never seen faster results in my life.

There are several Highland athletes that now train with them. I have met Pavel T. a few times, and been to some of his kettlebell classes in MN, the guy knows his stuff.

I confess that I have been delinquent in my training for the last few months, work is busy and we have a 7-month old baby crawling around. Time to make a new year's resolution...