The perfect reef fish should be "invert safe", peaceful, colourful, suitable for small tanks and as an added bonus it would be nice if they could be kept together. Does such a dream fish exist? Thankfully the answer is "yes"!
The Yellow coral goby (Gobiodon okinawae) lives in branching hard corals in the wild and will normally set up home in as similar a situation as it can find in the aquarium. Unlike clownfishes, their commensal behaviour is easy to duplicate in captivity and they'll perch in soft corals, large polyped hard corals and many other places that they'd never see in the wild state.
Gobiodon have interesting sex lives to say the least and can change sex to suit the social situation. Any two individuals of different sizes will become a male and female with the larger of the two assuming the male role. Should two males be placed together then the smaller will become female. Handy when you're a tiny fish in an enormous ocean!
Yellow coral gobies will eat a range of aquarium foods and are best fed little and often, especially if recently imported, as the light feeding regimes used to ensure they travel safely can mean that they lose a little condition in the process