A channel catfish is what my LFS suggested to me, but I myself recommended a schol of Clown Loaches to my brother for fun, but a Dempsey would be a nice tank mate as well, if tht's one of your top favourites, I'd go with that one.
First off the Carpintis I suggested is a texas. Second I have a blue channel cat and I love him. He is in my 55 right now. I have had him almost a month and he has grown almost two inches! They are supposed to hit well over a foot in the first year. I am transfering him to my 150 when it is done cycling but recognize he will probably also outgrow that. They are the common catfish you catch with chicken livers all up and down the east coast and can get up to 60 or so pounds! They eat up anything that will fit in their mouth. I will put mine in a pond when he outgrows my tank.
I would strongly recommend the geophagus they are beautiful fish, you can look them up on this site they are called pearl cichlids. They are realitively peacful and get to 10 inches plus. A red terror will not in no way no how work, he would shred your oscars, mine is only about three inches and attacks flake food with a passion. They are amphilophus festae similar to red devils, trimacs and midas...super agro.
