I have both a stand and a mounting arm.
Your options are pretty much anything mounts that will hold over 17 lbs for the 2012-2015 models, 2011 and older are 30 lbs.
If you aren't worried about aesthetics then Monoprice has a good selection of inexpensive stands and wall/desk mounts/arms.
If you want something prettier then I'd go with ErgoTron or ErgoTech, you can find an assortment on Amazon fairly easily.
I have several arms and mounts from Monoprice and they do their job well, they are just more of a plain look and black.
I also have an ErgoTron MX Desk Mount that looks very nice and gives more flexibility because it is a spring loaded arm that allows easy movement up down, tilting, left, right and portrait to landscape. It was the one I purchased for my 2009 iMac and it's rated up to 30 lbs so it can definitely handle the weight of the newer 27" iMacs.