I really did save the best for last, because this humble little sandbed goby is my favorite fish of all (*sshhh* don't tell the others :-). I'm not sure exactly why. It's partly because of the way it looks--an exotic green/orange/red pattern (much like the mandarin duck, which it is named after) and unusual shape (it has the coolest pectoral fins, almost like undulating fans that allow it to "hover" in mid-water).
Partly, it must have to do with its behavior. It is always busy doing its own thing, never bothering a soul, just a constantly moving hunter of small pods in the rock and sand. It looks like it is on a mission all the time, and ignores everyone else.
The only problem with mandarins is that they have a very exclusive diet. Very few of them will eat prepared foods, though I've heard of ones being coaxed to do so after years, this isn't usually an easy task.
Most will only feed on live pods and tiny shrimp, and so need to be in a large tank with a very active sand bed. I am able to accomplish this because I run a refugium on the back of my 60gal reef, which is brimming full of copepods, amphipods, and mysis shrimp. They reproduce so fast that there is a constant supply that gets sucked into the main tank daily, and I think my mandarin is healthy as a result. I would highly recommend this gorgeous little fish to anyone who thinks they can support their dietary habits.