I don't know how big it'll get but it defintely will get stunted. Not good for long term health. It will be much happier in a 55 gal by itself. The oscar can get upward to a foot or more. It'll need the room to turn in the tank.
This site has a great species list. Look around iam sure that you well find somthing else that well spark your intrest. Maybe a severum well be a good bet for your tank.