in a 90, with a tang, your possibilities are near endless, the only thing is that tangs can be aggressive towards anything added after them, so use caution when adding anyfish, but you can still do it
were you looking at adding several smaller fish, and a community tank?, or a couple of larger fish, or maybe even somethign a bit more aggressive? also, would you like a reef, or a fowlr, or a fo tank?
these q's can help to narrow down alot of fish, and make the decisions eaasier
personally i like a smaller community set up, my 75(same dimensions only a couple of inches shallower than a 90), and have gobies, blennies, cardinal and clowns in with my koles tang