Below are some ideas on standing and treadmill desks.
http://www.treadmill-desk.com/
http://www.wired.com/geekdad/2012/10/treadmill-desk/
http://iamnotaprogrammer.com/Ikea-Standing-desk-for-22-dollars.html
http://www.amazon.com/Trek-TD-01-TrekDesk-Treadmill-Desk/dp/B002IYRBI0