mentioned 3 exercises: wrist curls, spinning ball thing and i don't know what the 3rd is called (finger abductors?: expanding your curled fingers outward) in this thread

http://news.ycombinator.com/item?id=185743

http://www.fitter1.com/Catalog/Category/35/HandWrist.aspx

Make sure you don't cock wrists at funny angles when you're driving a car, using power tools, sleeping (don't sleep on your side). And elbow and heel of hand supported weight-wise at all times when working mouse and keyboard.