I recently got a Flexispot Adjustable Pro Series Standing Desk. Mine is the Willow Solid Wood Standing Desk, which has a 48" × 24" desktop and a height range of 27.9" to 47.6".
There are plenty of other options on their site, including standings desks for kids, gaming desks, and desks in many sizes.
I've been wanting a standing desk for quite a while now because of the health benefits; reduced back pain, lowered risk of disease, better mood, and better productivity.
My favorite thing about the desk so far, though, is that it's been so helpful to be able to raise and lower the desk when I'm working on a drawing. I place an angled drawing board (this is the one I have) on top of the standing desk, and it's super useful to be able to adjust the height of the desk depending on which part of the paper I need to have at my eye level. This feature is pretty great for artists. The desk moves up and down automatically when you press on the arrow buttons, and can be used as a normal, sitting-desk too if you get tired of standing.
Overall, It was pretty easy to assemble, all you need is a screwdriver. I work from home and have mild back pain, so it brings me some peace of mind to know that I'm taking better care of my body by using this desk.