You can make a stand-up desk from an old door and two sawhorses, customize a store-bought desk, or pay a company for a ready-made one. Here are some options:
Here are three examples of DIY options for making a stand-up desk: a sawhorse desk, a metal cart desk, and a plywood desk. If you are a serious woodworker, you can buy plans for a stand-up desk at Woodware Designs.
Ready-made stand-up desks
The Fredrik desk from IKEA can be put together to make a stand-up desk. IKEA also sells office table tops in various sizes and shapes to which you can add adjustable legs that telescope up to 42 inches.
If you like your office setup but want to add stand-up capability without adding more furniture, the Anderlyn Desk is a platform that sits atop a standard desk, creating a stand-up work surface.