There's big business in stressballs these days. You can hardly go to an office without seeing a few gathering dust on people's desks. The dust, of course, is an indication that they don't work. (Unless your goal is to develop kung-fu grip and have a really commanding handshake.)
But here's the secret: your job isn't stressful.
Don't get me wrong - your job is very likely demanding and difficult. However, the stress generally isn't inherent in the work you do. Rather, it's your reaction to the demands of the work. And if you're stressed, it's because you either lack the knowledge or the systems to deal with those demands. (However, if you're in one of those jobs where your company's very existence hinges on every decision you make (Aeron chair or Mirra chair?) feel free to skip this and go back to work.)
I met a guy recently who's a pilot for the Navy's Blue Angels. I asked him if the job is stressful - after all, flying wing-to-wing at 500 mph near densely populated areas doesn't exactly provide a large margin of error - and he said no. He said that he has the knowledge and the systems to do his job, so performing is just, well, routine.
I got a similar answer from a neruosurgeon I know. You'd think that poking around someone's brain with sharp instruments would be stressful - one slip, and the patient starts acting like Dustin Hoffman in Rainman. But he says that he has the knowledge and skills to do the job, and he has a system to ensure that he does it correctly.
Think about the first time you parallel parked a car. Or the first time you shaved, or tried to unsnap your girlfriend's bra - you lacked the knowledge and the system to do it well. Pretty stressful, right? And in the case of the bra, pretty embarrassing as well.
Most likely you have the knowledge you need for your job. (If not, talk to your HR department or your boss.) So the stress you feel is due to the lack of a solid system for dealing with it. In lean terms, you haven't created standard work. Consequently, when you're hit with mulitple (and often competing) demands on your time and attention, you get stressed.
Obviously, there's a huge amount of unpredictability and variability in your work, and sometimes the wheels on the bus are going to come off regardless of what systems you have in place. But establishing systems to deal with your workflow - e.g., habits to get your inbox back to zero, to reduce the daily interruptions, to delegate more effectively, etc. - will enable you to eliminate the "controllable stress inducers." And if you can do that, you'll work more efficiently and with less stress.
Or you can just buy another stressball.