The biggest obstacles were that I'm 6'4" tall and need a desk that can support 3 big monitors.
I ended up making my own (admittedly non on the fly adjustable) standing desk out of shelf track - the closet shelf system they sell at Home Depot or wherever.
My keyboard shelf is 40 inches high and the monitor shelf is 52 inches high.
Total costs were around $100 and it only took an evening to put together.
[EDIT] - Pics of build and final desk at - https://www.dropbox.com/gallery/3175742/1/StandingDesk?h=8d1...