When I'm all done getting all the fish I want and need... Magic Fish, the 21 "Perfect Fish"... I will sometimes sell off the rest to make room for extras of the ones that I want more than one of...that look prettiest swimming around in pairs or small groups.
For me, these would first be the most colorful ones, of course...the Canary Fire-Arrow, the Speckled Leaffish, the Crimson Comet. And I really love a few of the Razorback Carp swimming together in the same tank. They look so...normal and REAL swimming around in there! lol.
Then, for dramatic accent (and especially in the 2nd tank) either a few Silky Sharks (Orange Sharks look pretty sharp in there too), or a pair of Stubby Groupers.
The Oriental Flashfish look particularly pretty in the 2nd tank too, as the colors of the fins is picked up by the coral colors.
I know that the Bananafish is probably suppose to have the little white fins, but I think she looks really lovely with the Tiger fins. So I keep a few extra of those, if there's room.