I found this thread on Ask Metafilter. Hopefully it'll bring some relief for those of you with achy wrists. Some of the recommendations:

I love that Logitech Trackman. It saved me when I had tendonitis in my right wrist in late high school/early college. The thumb trackball takes getting used to but once you're good with it you're golden.

My strategy has been to learn all possible keyboard shortcuts, especially since I'm always on the road with a trackpad and no mouse. In a well-written program, the vast majority of functions can be accessed via keyboard, including buttons and popup menus. Also get used to using both hands for mousing. I feel the Dvorak keyboard also has helped---not to ignite the old religious war. I wouldn't say it's made me faster, but it is easier.

The rollermouse saved my frickin' life. They're about ~$100. I heart mine.