You might like to check out the FitDesk. It’s actually a seated cycle with a spot for your laptop. I have no official connection with them, but we reviewed it and found it to be quite effective. Here’s the link if you’re interested: http://funandfit.org/2011/05/fitness-desk-fitdesk/.
A standing desk is ideal for people with back problems who cannot sit for any length of time without severe back spasms. There is even an entry in Wikipedia about them: http://en.wikipedia.org/wiki/Standing_desk. I have known one person who actually rigged up his workspace with boxes so that he could work standing up.
Unfortunately, I do not have a recommendation as far as amanufacturer is concerned but there are many companies out there offering them.