I used to suffer from quite acute RSI. I am naturally suspicious of anecdotal reports of miracle cures, but for me at least a Kinesis keyboard pretty much solved my problem entirely. I'm much more conscientious than I used to be about posture, taking rest breaks and stretching, but none of that was as important in my case as having the right Keyboard.

I'm so paranoid about the company going out of business - they seem sort of small and niche - that I keep TWO spares at any time.