Fish to add to a nano cube?

I too would browse the nano section of liveaqauria.com. I had a shrimp/goby pair in my nano and loved to watch them Just be sure you choose a goby and a shrimp that pair up. It's pretty cool - the shrimp are basically blind so the goby keeps an eye out for predators, and the goby gets a home dug by the shrimp.

From your other post I see that you have a firefish in there. What is everything currently in your tank and how long has it been running? This will help us advise you better