Don't laugh. Giant Danios.
I know Giant Danios aren't much to look at as juveniles, but when they reach adulthood they blossom into colorful eating machines.
I keep 18 of them in a 120 g. long where they beat the tar out of Tiger Barbs and Buenos Aires Tetras.
At feeding time the Danios swarm at unbelievable speed. I have to grossly overfeed just to make sure enough food reaches the bottom level for the Loaches.