This is either one of the silliest ideas ever or brilliant - this ergonomic USB keyboard from Smartfish moves slightly every so often, depending on your workload, to keep your wrists from aching and help avoid repetitive stress injuries. It'll be available in mid-April for $150.
The two halves move apart and together and the base sort of vibrates subtly around once or twice an hour to massage your wrist muscles; the frequency depends on hard you pound the keyboard. Theoretically, you won't even notice the movement - see if you can see the varying stages of movement in the pictures. There's also a massaging mouse available.
It may work, but you'll need a lot of desktop space - the thing is pretty large.