As I may have mentioned before, I've been suffering with RSI in my left (non-mouse) wrist. I thought it would be useful to put a few links down to advice/tools/services that I've found handy.
Madgex got the lovely people at Posture People, a local company, to come in and visit me at my desk and do a workspace assessment. This involved recommendations, such as reorganise my desk, move my monitors, as well as the more practical element of adjusting my chair so that if offers support in all the right places. They also brought me an Ergo Rest wrist rest which I use on my left harm to support my wrist and keep my arm in the correct position.
I also ordered an ergonomic keyboard for the office.
As we use windows at work, I use workrave to monitor my use of the computer. It tells me when I should have a micro-break, or a rest-break, even providing optional exercises to do during the rest. The settings for how often are configurable, but it provides a good method of ensuring I don't get too carried away when I should be stepping away from the keyboard.
At home I use a laptop, but do at least have desk space for it. I bought an external keyboard, and a laptop stand to enable me to raise the laptop to approximately the right height.
In a similar vein to workrave, there is a tool called AntiRSI for the mac world. It doesn't provide exercises, but it does still offer the concept of micro and rest breaks.
I have also been visiting an osteopath which, combined with all of the above, has made a difference to both my wrist issue, and a persistent ache just behind my right shoulder blade.
There are some excellent blog posts, and advice sites out there, just search google. The blog post 10 ergonomic tips for setting up your home workstation gives some good, and generally easy to implement, suggestions and deserves a read even if you currently don't have any symptoms at all. Prevention is better than cure and all that.