Love my trackball!!!! I was getting elbow and wrist fatigue bad when I played poker online for 4-5years. I'm sure I was headed for carple tunnel. Got a trackball and never looked back.
I use this one http://www.amazon.com/gp/aw/d/B001F4...dir_mdp_mobile
Not the fanciest or most expensive, but works. I have one that is around 6 years old, and it's still going strong.