Excersise while at a computer? (Under desk stationary bike pedals)

FatPixiee

So I spend hours and hours a day at my computer. I remember hearing someone mention that they had an under desk stationary "bike" for work. I think that would be a great idea. Does anyone do this or know what kind of machine would be good? I just want to be doing something physical instead of just sitting on my butt motionless.