I had the worst back pain for 15 years (been programming since the late 80s, lots of desk jobs...) until I saw an article about standing desks. I looked a few up and ended up buying one called the Kangaroo (it's adjustable and just sits on top of your current desk) and I loved it! I ended up buying a better one for work, and a more portable one for my wife. It relieved my back pain so much I decided to make a site, www.beststandingdesks.com, about my experiences so other people could learn.
If you have any questions about my experiences with a standing desk, just email me.