One of my all time favorite fish is the tailspot. See my avatar. That said, how about a neon goby. This is also a great fish, especially if you can get them as a pair. I love the pair I got a few months ago. Great personality and very tight pair bond. They are constantly together. They would be great in a small nano. The tailspot, not so great in that size tank. They are best in an environment where they can graze all day long on lots of live rock.