Okay, not just for leg-bobbers, but a simple inexpensive generator that you could work with a foot pedal while you sit and type. It's a way to burn calories while sitting at your desk, it's a way to reduce your carbon output (you can easily charge your cellphone with an hour's foot pump), it let's you feel less guilty about your sedentary desk job. I think better when my leg bobs, so it could also be a productivity tool to boot. Get it? Boot?
Don't mock me, I'm a new dad with fewer brain cells than before, I'm allowed corny jokes now. But seriously, simple foot pump DC generator with adapters for cellphones, laptops, USB equipped (for devices that run off USB power like small fans, LED lights, etc.).