Price: Kinesis Advantage, $299; Microsoft Natural Ergonomic Keyboard 4000, $50
Besides mousing around, the number one thing you do while at your computer is type. This, as you probably know, can become incredibly taxing. The best way to alleviate some of the pains and fatigues associated with prolonged typing is to use an ergonomic keyboard. Now, depending on how much coin you're prepared to drop, there are many options on the market.
At the top of the line is the Kinesis Advantage (Yes, that's the keyboard Will Smith used in Men in Black). Split and deeply contoured, it looks like nothing else on the market. And that's the point. It will take a little while to become accustomed to typing on one, but once you do the benefits are very noticeable.
If you're not trying to spend $300 on a keyboard, there are cheaper, less effective alternatives like Microsoft's Natural Ergonomic Keyboard 4000 which retails for $50. But, just know you get what you pay for.