I’ve been standing up at work for a couple years now; not consistently, but more often than not. I’ve had different computers and furniture, but nothing permanent.
I stuck an iMac in a bookshelf:
I stuck a MacBook Pro on a bookshelf:
I precariously balanced that same MacBook Pro on a railing when I wanted to work outside:
And at my current job, I’ve been using a stack of cardboard boxes:
I’ve been using that stack of boxes for a year, and I was getting a little sick of it, so I decided to spruce things up a bit. I’ve had a few shelves that I picked up at Ikea years ago and stained (very) poorly; those have been sitting on top of the boxes to provide some stability. I painted them a delicious green and added a keyboard shelf, and voila: