Good luck with the stocking - it's always hard with cubes, since they can't accommodate the kind of large fish their volume might indicate.
I'd second the angel suggestion. Tall fish look good in tall tanks, and the common pet store angel is popular for a reason. If you want fancy, more expensive fish, there are a lot of "strains" bred for a specific look.
You could also do loaches, the tank is not quite big enough for clowns but yoyos, dwarf chains, skunks, zebras, kubotais etc. should be fine. They're interactive fish and will make full use of the height of the tank, but they are best kept in large schools (they can even become depressed or psychotic out of stress if prevented from interacting with their kin). Horse headed loaches are another option, but they're specialized for "swimming" under the sand, so if they're happy you will rarely see them.
Also consider a pair or trio of three-spot gouramis. If you want oddballs something like a puffer colony would work, as would Channallabes eel catfish (if you want to make the Americans jealous - they're common enough in Europe, but banned in the US), ropefish, or leopard ctenopoma.