Although TIME blogger Lisa Takeuchi Cullen doesn't seem to be all that interested in the idea, I'm rather intrigued by the Steelcase Walkstation, a desk set that replaces the seat with a treadmill. By adding even a modest amount of physical activity to everyday activities, workers can burn more calories than just sitting would otherwise require. Steelcase even purports that the activity may offer "less stress, increased productivity and improved focus."
Steelcase is hardly the first to discover the idea; I even tried something similar last year with an elliptical machine, although I discovered that it takes too much effort to type while bouncing up and down to be truly productive. You can even buy little pedals for under your desk for less than $50, far less than Steelcase's projected $6,500 for the Walkstation.
The ultimate solution, of course, would be a way to use the energy expended while walking at your desk to trickle charge gadgets.