Many people are using standing desks to work in a more active fashion. The Halter ED-258 Sit / Stand Desk is another solution for those of you who prefer working off your chair. It comes fully assembled and has handles you can squeeze for height adjustment. You can fit it on most desks.
The Halter ED-258 Elevating Desk has a max load of 20kg. It lets you switch from sitting to standing in seconds. Costs under $300 at this time.