Although this is an old thread I would like to mention that with a 10g size limit there are still a few fish that would work nicely. For tiny but unusual fish there are pygmy sunfish such as the Okiefenokie sunfish. The leopard ctenopoma is barely feasible while the African butterfly really needs more room.
My vote for a tank of this size would be either a breeding pair of Lorentzi puffers, or a pair of either black-banded or blue-spotted dwarf sunfish with a nice small cat such as a S. petricola.