I've haven't really decided on a "center piece" fish. Each of the fish species I am planning on is awesome in its own right, but smallish. The T. espei (lambchop) that I have ordered only grow to about 1.5 inches. However, they are more colorful than the larger T. heteromorpha (harlequin rasbora) that are so much more popular. Look at the different coloration between the espei and heteromorpha. Big difference.
Lambchop (T. espei)
Harlequin (T. heteromorpha)
Next are the corydoras. Again, I worked really hard to find the perfect mix of size and coloring. I like the smaller species, because that allows me to get more individuals and the animals can show off more of their "natural" behavior (at least I as understand it). The dwarf cories are far more interesting looking than the other two smaller species of corys and spend far more time in the bottom of the tank. Notice that the habrosus has the traditional cory shape, while the others don't really have it quite the same. The others also spend much more time in the mid-water than the habrosus. Unfortunately, I don't think I'll be able to get the habrosus for several months. They aren't in at the fish store where I am getting the T. espei, nor are they available for that store to order just now.
Salt and Pepper corys (corydoras habrosus)
pygmy corys (corydoras pygmaeus)
corydoras hastatus
My next big decision is which of the other shoaling varieties I am going to go with. They have to be peaceful and calm enough not to spook the other fish. Five banded barbs might be a bit too low in the tank. Black Phantom Tetras might be a bit nippier than I need. Bloodfin tetras might be too big for the rasboras. I'm starting to think guppies, believe it or not.
Then there is the cichlids... They look so great, but I'm not sure if having them in my tank breeding would be dangerous to the corys or not. I've still got months to go before all this matters. I still could go with some honey gourami or something similar. Maybe even bleeding heart tetra, they are bigger, but aren't very active. Months from now, who knows what direction this will end up going.
Maybe I don't need a "center piece" as long as each piece is interesting enough in its own right.