Theres clowns of course, you can do designer clowns to be different. Also a goby and blenny would work out fine too. Like said above maybe a pygmy angel fish...even a wrasse woudl work since its a covered tank. But I would limit it to about 4-5 fish tops. I'm overstocked in my cube now with 6 fish, but 4 of them arent swimming fish, just perchers or burrowers or just plain sandbed fish. I only have the two clowns that utilize the whole tank.
I would also say add some shrimp, I have a cleaner and three peppermints and some emerald crabs are cool too.