Dotty backs are semi-aggressive and can be territorial, which might be even worse in a tank that size. Clowns are very cute, I have a black and white clown. Firefish are nice. I have a dwarf half-black angel in my tank he's done fine, but he does like to swim in and out of all of the caves that I have in my rockwork. Angels also tend to pick at corals, just in Case your planning to add coral later, might wanna keep that in mind. Blennies are cute, have a lot of personality, but don't really swim around a whole lot; mostly tend to sit on the rocks. Dartfish look nice. The white stripe Pygmy wrasse is pretty and colorful. If you go on liveaquaria.com, there's all kinds of fish along with tank size and temperament. Personally, I have only added fish with peaceful temperaments cuz I didn't want any fighting or killing goin on. A sand-sifting fish is cool to watch. Just some random thoughts.