I was on a similar hunt, and have chosen my fish, but have yet to find one to buy. I was repeatedly told that a yellow clown goby is perfect for tanks in the 10-gallon range. Reef-safe, hearty, colorful, full of personality, and gets along with everyone. My tank has been fishless for a loooong time waiting for one of those.
Cool fish, I loved mine, but there is a good chance they'll nip SPS and also they are pretty small and fairly stationary. I had mine in a 19L (5 gal) pico tank and it didn't 'fill' the tank.
I would go something very unusual. Either a Tanaka's Pygmy Wrasse or a very fancy variant of a clownfish