[gojomo]

A comparable commercial offering, made for this purpose and also mounting atop an existing desk, would be the Ergotron Workfit-S, costing about $370:

http://www.ergotron.com/tabid/640/Default.aspx

For the extra $350 you get easier/finer adjustments and perhaps, more stability.

For someone who just wants to get a little standing time in with a laptop, an adjustable 'over-bed' table for about $50 is almost a good solution:

http://www.amazon.com/gp/product/B000QA0EHI/ref=oh_details_o...

I say almost because it doesn't quite have the rigidity that would be best, or ability to handle any leaning/weight other than just light hand placement.

[mceachen]

I got one of these last year.

Even on a really stout desk, the keyboard tray and flimsy plastic display mounts caused the whole assembly to wobble about whenever I typed.

I switched back to my trusty wooden box after only one day: https://twitter.com/andrewrow/statuses/180759221443371008

[apinstein]

I bought one of these last year, it's really nice. Easy to switch between sit & stand, and you can even use it with a laptop just by adding an external keyboard.