I had Silver Dollars with my Oscar in my 55 back then. Also if you want to or can only go with basic pet store stuff I also recommend (from my experience) Dinosaur Bichirs (make sure you separate them if the Oscar grows faster or else it will get attacked), Common Pleco (again from my experience, but for you a Royal Pleco would be cool, one of my dream fish), Striped Raphael Catfish, Large Syno Catfish, Pictus Catfish, and something like other Cichlids or Catfish.
