I've had my Varidesk Pro Plus 36" ( http://www.varidesk.com/ ) for about a month and I love it. They are relatively cheap, ~$350, easily adjustable, and I even got the boss the pay for it.
I've been sitting in front of a computer for a living for about 25 years now and definitely have my share of back issues. So far, I've worked up to alternating standing and sitting for 30 minutes at a time, although I sometimes get tired by about 3pm. Overall, the Varidesk is a great improvement over sitting all day, and I've not personally found any problems working/coding from a standing position.