If you’ve ever had trouble with tendinitis, as many programmers and PC gamers do, one of the best things you can do is replace the mouse with a trackball. It takes a little practice to get used to it, but it’s actually much faster than a mouse.
Alas, one of the best trackballs ever made, the Microsoft Trackball Explorer, is no longer in production. I see them selling for $130 on eBay now.

If you have an old one, it may seem sticky. That’s easily fixed. First, periodically you should blow or scrape the lint out of the small metal bearings that the red ball rests on.
To keep the trackball working perfectly, occasionally cover the ball with a very very tiny amount of vasoline. The ball should turn for one or two seconds when you spin it.