Pseudomugil - the entire genus. They are small rainbowfish, largely Australian but some species from New Guinea. They are small (3-6cm) peaceful, active, eat anything, will breed in the community, fry are easy to raise, and are extremely colourful. What more could you ask for a community fish? But the only species I have ever seen in the trade are P. signifer (the most common and people often fail with it because it needs brackish water) P. gertrudae (people are scared off because it's so small) and P. furcatus, which is not as colourful as many members of the genus. These are TOTALLY unappreciated... the most beautiful of them are P. connieae which I have never seen, and P. mellis which is a temperate fish and can be kept unheated. They are called 'blue eyes' but most don't even have their own common names.
Diamond tetras - as juveniles, seen in overcrowded dealer's tanks, they are BORING, apparently no colour and a completely unremarkable tetra. You have gotta see an adult well settled in a tank.
The same goes for most rainbowfish, as juveniles they are colourless, an ugly grey shade usually, and they do not show colour until they grow up and are happy with their environment.