IMHO the Kinesis Advantage is the Rolls Royce of keyboards. After having used it for over a year, I can't imagine going back to anything else.
It takes a couple of days to get used to it (the keys are not diagonal like in a standard keyboard, and it takes a little while for your muscle memory to adjust). By the way this will really improve your touch typing if you don't have proper form (since the keys are contoured to the shape of the hand there really is no way to type but the right way).