if your tank have a nice cover to prevent fish from jumping... firefish , flame gobies...are cool fish for you... another suggestion yellow head jawfish ... all these are mild mannered fish and will not require a bigger tank in future...
You can keep an pigmy angel , but with time may pick up your clownfish... flame angel, coral beauty would also be fine , but may pick your clown also...
A pair of Banggai cardinal would also be fine and you may even breed them... if you like blk/white fishes ...
any other fish will require new tank sooner or latter ...so choose wisely...