I built an elevated platform so I could try working at a standing desk. It's 11.5 inches high, and I built it from .75" x .75" sticks and .5" plywood. I added lots of triangular bracing and then sat on it to make sure it could hold my 27" iMac without collapsing. I just started using it this morning so I can't say how much I like it yet.
This is a prototype. I am going to use this one for a week, take notes, and make another prototype. (First note for Prototype 2 - a nook under the plywood to hold the external drives and USB hub.)
Here's Donald Rumsfeld at his most charming (which is about as charming as a monitor lizard) defending his standing desk and explaining to the CNN host that Thomas Jefferson had one and that naval officers use them. Go Rummy!
UPDATE: Here is the image I'm using on my desktop.