I work in Environmental Health and we get requests to perform an ergonomic evaluation all the time. Most of the time people call us thinking that we'll simply be able to get them a more expensive chair and that's the extent of what's required to work ergonomically. First, get out of the mind-set that you need to spend a lot of money to create an ergonomic work environment. Many people think that in order to have a workstation that is "ergonomic" then you need to have a piece of furniture that's been stamped ergonomic by the manufacturer. But that's simply not the case; you can create a completely ergonomic work setup with standard furniture without the need to pay a premium to buy an "ergonomic" workstation. You can do a lot to improve the ergonomics of your workstation by simply rearranging where you keep your equipment. If you have your monitor to your side so you constantly have to look over when you type, then move it in the middle. The top of the monitor should be at your eye level (it's more comfortable to look down slightly while you're typing than it is to look up or straight ahead for extended periods of time). If you're constantly leaning over to see your screen, bring it closer to you. Try and get away from wrist-rests; despite what you might think, having your wrists constantly sitting on those "ergonomic" wrist rests is actually terrible for your wrists and your typing technique. If you spend a lot of time on the phone, use a headset instead of picking up the phone and awkwardly holding it in place with your neck. Make sure your feet are flat on the floor...really all you need in a good chair is firm lumbar support and the ability to adjust its height so your legs aren't dangling or bent awkwardly (use a footrest if you're short and can't touch the ground with the chair all the way down). Buy a simple document holder to hold documents you are reviewing while you work, rather than have them laying flat or holding them in your hands. Take frequent breaks from your work (5 minutes every hour is usually recommended). This all will work wonders to improve your productivity and also reduce your risk of developing any type of repetitive motion injuries.

It is true that standing up, at least part of the time, can be a healthy improvement over sitting for 8-10 hours a day. However, I am unaware of any study showing that standing for the entire time is necessary or even desirable. That is the reason for the recent popularity of the adjustable desks, that can be changed from sitting height to standing height. They are much more popular than standing-only desks although quite a bit more expensive, too.