Medicine balls are really fun and can be a good alternative to hand weights. I like them because they are easy to hold and keeps my fitness interests up and boredom levels down.  They are especially good for increasing core strength, improving balance, and improving coordination.  Also, they can simply just take you back to your childhood where you can throw, toss, and slam it!  They come in different weights, but I think 6lbs is a great place to start!