I second that. A salvini would do pretty good in a 75 by itself or maybe with a mate in a species only setup if they tolerate each other. Another option would be acaras but I don't think they get more than 6 or 7". Angelfish would be cool too.
Maybe one baby oscar would do ok in it as a growout tank with no tank mates and massive maintinance. Be aware a full grown one would have no room so you would have to upgrade asap.
If you want something smaller, livebearers maybe? Could get some huge sailfin mollies and set it up as a brackish tank. Or pike livebearers in a group would be pretty sick if they are legal where you live. (Mad that they aren't legal here for whatever dumb reason, dammit commiefornia!)