There has been much discussion about the benefits of standing while working at a computer, but not many well-made solutions for a combined sit /stand-capable desk. Ergotron, Inc., a Nortek Company, has solved the desk problem with its announcement of two new Sit-Stand workstations designed just for Apple computer users.The WorkFit comes in two models, the WorkFit-A for desktop iMacs and the WorkFit-P for MacBook users. Both silver, solid-aluminum Sit-Stand Workstations are designed to compliment your Mac computers.
The WorkFit A (US$649.00) "includes arm, work surface, base, keyboard tray support, keyboard tray, desk clamp, grommet mount, assembly fasteners, cable management hardware [and] adjustment tools." Its maximum capacity is 25 lbs (11.4 kg), which easily accommodates the 20 to 22 lb weight of the iMac from late 2009 to present, plus keyboard and mouse.
The WorkFit P (US$329.00) attaches to your existing desk and provides a stand or an extra work surface. The WorkFit P "includes arm, work surface, pole base, desk clamp, grommet mount, assembly fasteners, cable management hardware, [and] adjustment tools."
You can read more about the benefits and perils of sitting and standing at your computer on many websites, but I think the Cornell University Ergonomics Web and the UCLA Ergonomics sites cover the issues briefly with good information to help you make an informed decision as to whether standing is a good option for you. No matter which option you choose, the Ergotron workstations have you covered.