Then what about a blenny or some clowns? Royal grammas are nice and colorful too. You could also get pygmy angels too. They are awesome. You have a huge choice since you arent reef. But you can't go crazy, still a small-ish tank. lol
Check out liveaquaria.com they have like every fish and decent descriptions too
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.