Information provided by: Medical Billing and Coding.
Above: a portion of an infographic titled "Sitting it Killing You." I've been using a standing desk since April 18, and I love it. I just bought a gel mat this week, and now I'm even happier standing up all day.
UPDATE: A couple of people have e-mailed me to ask what kind of gel mat I bought. I got mine at Costco for $23.99. I'm sorry to say I removed the manufacturers tag so I don't have any additional information about it. I looked at the Costco website but it doesn't seem to be available online, although Costco online does offer a number of other anti-fatigue mats. Here's a photo of the one I bough (above). I've only been using it for a day, so I can't give it my full recommendation yet. So far, I have been enjoying it.