Medicine balls are a great addition to any workout, esspecially in the martial arts. I imagine just about every boxing gym has a bunch of them lieing around, but martial arts clubs often lack them. They are great for ab work, plyometric training, and general next morning soreness inducing. Problem is, they can get pretty pricey, so here is a easy, cheap alternative that makse a good, sturdy medicine ball. http://innovativema.ca/forum/view.php?pg=buildamedicineball
Although I've seen it before, you have now inspired me to make one up this weekend Great idea and you can't beat the price. There are probably schools that will want to throw away popped or knackered old basketballs too so you could get it for even cheaper.