From Wikipedia:

Ergonomics is the study of designing equipment and devices that fit the human body, its movements, and its cognitive abilities.

In other words, your mind works better when your body isn't being abused.

Keyboards

• Das Keyboard (for those of us who crave mechanical key switches). The keyboard of choice here at DevRoadmaps. Check out the Das Keyboard blog.
• Microsoft Natural Ergonomic Keyboard

Chairs

• Read Jeff Atwood's classic blog post on ergonomic chairs. "In fact, after browsing chairs for the last few years of my career, I've come to one conclusion: you can't expect to get a decent chair for less than $500. If you are spending less than that on seating -- unless you are getting the deal of the century on dot-bomb bankruptcy auctions -- you're probably making a mistake."
• The Herman Miller Aeron chair has long been the Cadillac of task chairs (at least, if you're old enough to remember when the name Cadillac meant something...).
• More recently, there's the Herman Miller Mirra chair.