How about a leopard ctenopoma or a single archer fish. Both are interesting fish and should fit well in a 75 gallon.
The cteno could be a little shy but give them plenty of plants for cover and they will feel more comfortable. I used to love to watch mine hunt for ghost shrimp. I currently have a single freshwater archerfish in my 55 and he's always out swimming around. His staple food is pellets but I also buy him live crickets to spit at.