you could try an African butterflyfish....(not very active, but an awsome looking specie) or you can try a glass cat fish...mine stays towards the top of the tank.
I would HIGHLY reccomend 5 or so "Flying Barbs" Esomus danricus, they stay at the top of the water majority of the time and are very cool to watch, they are very fast, and their pectoral fins are like the SW flying fish how they are big and flat to glide. Usually mine are at the surface with their mouths at an angle like they are looking out of the water.