there's alot of geophagus species that makes great oscar tankmates.
they live on the bottom of the tank. as we all know oscars are messy when they eat. geophagus keeps the tank clean:)
i've got Geophagus steindachneri and Geopagus sp. Tapajos "Orange head" in my
tanks.

I have got three Jurupari and they spend most of their time sifting through the sand. They are like little machines, you can see the sand is going in their mouth and coming out of their gills, quite fascinating to watch

i have a geophagus dicrozoster in one of my tanks. hes a little bulldozer constantly moving the substrate around. imo they are great mates in an oscar tank and should be listed as such.