I've been thinking of a themed nano-tank... I really like the little community living in my Pocillopora- both an "acro" crab and a small goby (I'm thinking its a Redhead Goby- Paragobiodon echinocephalus).
Coral choices could be Pocillopora, Stylophora, Acropora, etc. Choose a single, large colony (preferrably with an "acro" crab already in it). There are several coral gobies to choose from; Citron Clown Goby, Green Clown Goby, Panda Goby, or some other from the Gobiodon or Paragobius families.
Just a thought...