The Biomorph desks are not inexpensive, but they are the highest quality ergonomic desks I have found. Nothing cheap or flimsy about these desks. Very adjustable. Very nice to work at.

Be sure to invest in a high quality ergonomic chair and an adjustable foot rest. Stay away from "comfy" high-back executive tilter chairs. I invested in a top of the line clerical style ergonomic chair by Steelcase.
 

This split keyboard from ErgoCanada was a big help. The key pads are positioned at 45 degrees... very close to the natural position of your hands for typing. I also repositioned the numeric keypad to the left side allowing me to put the trackball close to the keyboard, reducing the "reach distance" to the mouse.
 

I have tried quite a few different trackball mice. The MacAlly Optical Trackball and the Kensington TurboBall are the ones I like the best. The designs allow you to curl your hand around the mouse and trackball in a natural position.

Be sure to use a wrist support mouse pad so that your wrist is correctly positioned when using the mouse.
 
Wrist braces are a must for me. If I don't wear them while keyboarding my wrists start to hurt after a few hours. Because I tend to sleep with my wrists bent, I wear braces at night to keep the wrists straight while sleeping.

The local pharmacy store has a huge selection of wrist braces, but only one model that is actually comfortable to wear.

Champion Plus 8" Wrist Splint 1083
distributed by Airway Surgical Appliances Ltd. Napean, Ontario, Canada
 
This device from ErgoCanada looks like something you'd buy while watching a late night informercial. My wife laughed at me when I showed it to her and admitted what it cost. I stop at 10 & 3 every day and use the arm aid. It helps to loosen the muscles and improve blood circulation. (I think it makes a difference.)