i am guessing by your lighting that you are a FOWLR system.
i would like to know if you are planning a reef.
if you plan to go reef or not , i suggest firefish (a shoal?), cardinal fish, chalk bass, a shoal af chromis (very cool IMO), coral beauty,
scooter blennies,
watchman goby, or another clown of the same species will be fine as long as you confuse the existing one by a little rearanging prior to addition.
the amount you can keep also depends on your reef status, IMO you can push your luck a bit more with fish only tanks. for reef application i would shoot for no more than 10 specimens in your 90g. especially if you are going to keep large fish like tangs.
i am not the duece bigalow type, but many would state that your tank is too small for more than one tang. they get a little fussy from what i have heard.
if your wife gives you any guff, tell her to get her own tank
