[I've written a few variations of this post over the years, so why not write it once in my journal here and just link to it]
The Kinesis keyboard has done nothing less than save my career. While starting a company in 1995 the long work days took a toll on my hands. After seeing doctor after doctor and specialist after specialist the best advice they could offer was "type less." Thank you very much, but I had deadlines to meet.
Everything changed when I splurged $300 for the Kinesis Contour keyboard. There are four major differences between this keyboard and the others out there, and together they make typing feel to me like I'm running down hill.
1. Separated "key wells" (you have to see the picture to understand) which allow a much more natural hand position.
2. Keys are lined up directly above each other (i.e. the T key is directly north of the G key, not up-to-the-left). This makes your fingers extend out and back, not out and back and side to side.
3. The key wells are curved, which brings the keys on the upper and lower parts of the keybard closer to your fingertips. This is probably the single largest factor contributing to the "running down hill" feeling.
4. Thumbs. Your thumbs are the two strongest digits on your hands. I don't know about you, but the way I used to type I would only use one of my thumbs, and only for one key (the space bar). My left thumb sat dormant. What a waste! Additionally, two of my most actively used fingers were my pinkeys due to the RET, Backspace and Control keys. Guess which fingers are your weakest? On the Kinesis, the thumbs get the most commonly used keys. I've got a couple of buttons re-mapped (due mostly to Emacs usage patterns) so the four major thumb buttons are Control, Alt, Return and Space. I couldn't live any other way.
Give it a try. You won't regret it.