Rollermouse

If you have ergonomics problems with mice, look at the Rollermouse.
I got it after my neck problems early this year, and I like it. For one thing, I no longer have to carry the weight of my arm when I use the pointing device.
It's not perfect, it's a bit pricey and if one has a very large screen (I have a 30-inch one), the cursor often can't go all the way across without reaching the limit of the roller bar's travel, and then it will zip the rest of the way, out of control. (This can theoretically be handled by upping the tracking speed, but this makes the cursor hard to control too.)
I have not made A/B test with a mouse, but I feel I like this. It takes a bit getting used to before you get good control though.
The Pro model has a very long roller bar, and my right hand will sometimes rest on when I'm typing, making the cursor jump around on the screen. It can be minimized by careful shifting of the keyboard's position, but I wonder if the non-"Pro" model would have been better for me. (Update: it is, though harder to find.)