In a tank that short despite it having 2 feet to it i'd still stick to the smaller tangs.
Are you going reef or FOWLR? Either way you may get away with a nice angel. If reef I'd lean toward bellus ..
Maybe a butterfly? again the species depends on where you want to go with your tank.
and no tank is complete without a blenny of some kind! I recommend the tailspot or sailfin or midas. Just be sure to have a tight fitting lid if you go with a midas or any type of jumper.
Heck you could even have a somewhat deeper sandbed and keep a garden eel, engineer gobies, jawfish, or some shrimp gobies to burrow under the rock.
I'd just avoid anything that gets too big or needs lots and lots of swimming room. Some anthias would probably do just nicely in a tank like that.
