Anything thats big enough to not be eaten and can stand up for itself should be fine as long as it suits the water conditions (ie no africans with them).
I have an Oscar, Sev, Silver dollars, Plec, Bichir and Syno in my 460L and they all get on fine.
Acaras, Dempsies, Firemouths, various Eels, some of the larger dithers (giant danios etc but they may become a snack eventually) and most bottom feeders that get a decent size should be fine- as long as your Oscar permits tank mates, not all do.