Frontosa grow slow enough that they can live quite happily in a 90 gallon for a long time, but eventually they will reach a point where I must agree with wuvmybetta - a 90 gallon is just no place for a harem of 8" to 12" Fronts. A 90 is enough for one 12" fish, if that.
If you are looking at having just one big fish then Oscars are great, as are Red Terrors, Managuense (Jaguars), and most of those large sized new world cichlids.
If you want more then one then you will want to go with a smaller type, like Firemouths (beautiful and pretty peaceful), convicts, jack dempseys, green terrors, severums, texas etc. Most of these would be limited to pairs, even in a 90, but you can probably get away with 1 specimen of 3 species.
Then, if you expand and start to look at other African cichlids (besides Frontosa) your options can really open up, but they are a discussion on their own.